「WHERE句でPOVをいくつかに絞る場合など、多くの場合、ORよりINの方が速いです」とユーザーさんからコメントを頂いたので、なんでそうなるのかな?と思いましたので、EXPLAINで実行計画を確認してみました。

まず、たくさんのPOVをORで指定した場合の実行計画は以下のとおりです。
ap2=# EXPLAIN SELECT '<img  src="http://pics.dmm.co.jp/digital/pcgame/' || gamelist.dmm || '/' || gamelist.dmm || 'ps.jpg">' AS 画像 ,'' || gamelist.gamename || '' AS タイトル ,gamelist.sellday as 発売日 ,CASE WHEN brandlist.url IS NOT NULL THEN '' || brandlist.brandname || '' ELSE brandlist.brandname || ' (解散)' END AS ブランド ,gamelist.median as 中央値 ,gamelist.count2 as データ数 ,(CASE WHEN gamelist.dmm_subsc IS NOT NULL THEN '有' END) AS DMMプレミアム ,SUM(CASE WHEN povgroups.pov=33 THEN 1 ELSE 0 END) AS 萌ゲー ,SUM(CASE WHEN povgroups.pov=10 THEN 1 ELSE 0 END) AS コメディ ,SUM(CASE WHEN povgroups.pov=57 THEN 1 ELSE 0 END) AS シナリオいい ,SUM(CASE WHEN povgroups.pov=193 THEN 1 ELSE 0 END) AS 主人公強い ,SUM(CASE WHEN povgroups.pov=50 THEN 1 ELSE 0 END) AS ロリ ,SUM(CASE WHEN povgroups.pov=314 THEN 1 ELSE 0 END) AS 戦う女の子 ,SUM(CASE WHEN povgroups.pov=369 THEN 1 ELSE 0 END) AS 女装 ,SUM(CASE WHEN povgroups.pov=379 THEN 1 ELSE 0 END) AS 主人公モテモテ ,SUM(CASE WHEN povgroups.pov=1 THEN 1 ELSE 0 END) AS おかず ,SUM(CASE WHEN povgroups.pov=13 THEN 1 ELSE 0 END) AS 主人公素敵 ,SUM(CASE WHEN povgroups.pov=216 THEN 1 ELSE 0 END) AS アナルSEX ,SUM(CASE WHEN povgroups.pov=250 THEN 1 ELSE 0 END) AS 陵辱レイプ ,SUM(CASE WHEN povgroups.pov=124 THEN 1 ELSE 0 END) AS 女の子に襲 ,SUM(CASE WHEN povgroups.pov=3 THEN 1 ELSE 0 END) AS ゲーム性有 ,SUM(CASE WHEN povgroups.pov=34 THEN 1 ELSE 0 END) AS キャラ取巻く世界観 ,SUM(CASE WHEN povgroups.pov=235 THEN 1 ELSE 0 END) AS 奇人変人 ,SUM(CASE WHEN povgroups.pov=72 THEN 1 ELSE 0 END) AS 主人公ダメ ,SUM(CASE WHEN povgroups.pov=528 THEN 1 ELSE 0 END) AS 個別ルートダメ FROM (gamelist INNER JOIN brandlist ON gamelist.brandname = brandlist.id) INNER JOIN povgroups ON gamelist.ID=povgroups.game WHERE gamelist.median >= 70 AND ((gamelist.count2 >=80 AND gamelist.sellday >= '2008-01-01') OR (gamelist.count2 >=40 AND gamelist.sellday >= CURRENT_DATE - interval '6 month')) AND (povgroups.pov=33 OR povgroups.pov=10 OR povgroups.pov=57 OR povgroups.pov=193 OR povgroups.pov=50 OR povgroups.pov=314 OR povgroups.pov=369 OR povgroups.pov=379 OR povgroups.pov=1 OR povgroups.pov=13 OR povgroups.pov=216 OR povgroups.pov=250 OR povgroups.pov=124 OR povgroups.pov=3 OR povgroups.pov=34 OR povgroups.pov=235 OR povgroups.pov=72 OR povgroups.pov=528) GROUP BY gamelist.sellday,gamelist.count2,gamelist.median,gamelist.dmm,gamelist.id,brandlist.url,brandlist.brandname,gamelist.dmm_subsc ORDER BY gamelist.sellday DESC,gamelist.count2 DESC;

                    QUERY PLAN

----------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------
 Sort  (cost=65952.58..65973.13 rows=8217 width=355)
   Sort Key: gamelist.sellday DESC, gamelist.count2 DESC
   ->  GroupAggregate  (cost=64206.29..65418.30 rows=8217 width=355)
         Group Key: gamelist.id, brandlist.url, brandlist.brandname
         ->  Sort  (cost=64206.29..64226.83 rows=8217 width=126)
               Sort Key: gamelist.id, brandlist.url, brandlist.brandname
               ->  Hash Join  (cost=11426.17..63672.01 rows=8217 width=126)
                     Hash Cond: (povgroups.game = gamelist.id)
                     ->  Bitmap Heap Scan on povgroups  (cost=9403.99..60155.36 rows=376612 width=8)
                           Recheck Cond: ((pov = 33) OR (pov = 10) OR (pov = 57) OR (pov = 193) OR (pov = 50) OR (pov = 314)
 OR (pov = 369) OR (pov = 379) OR (pov = 1) OR (pov = 13) OR (pov = 216) OR (pov = 250) OR (pov = 124) OR (pov = 3) OR (pov
= 34) OR (pov = 235) OR (pov = 72) OR (pov = 528))
                           ->  BitmapOr  (cost=9403.99..9403.99 rows=408734 width=0)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..344.66 rows=18164 width=0)
                                       Index Cond: (pov = 33)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..391.88 rows=20726 width=0)
                                       Index Cond: (pov = 10)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..1231.64 rows=65495 width=0)
                                       Index Cond: (pov = 57)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..386.18 rows=20500 width=0)
                                       Index Cond: (pov = 193)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..357.75 rows=18842 width=0)
                                       Index Cond: (pov = 50)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..351.49 rows=18541 width=0)
                                       Index Cond: (pov = 314)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..106.05 rows=5549 width=0)
                                       Index Cond: (pov = 369)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..439.66 rows=23364 width=0)
                                       Index Cond: (pov = 379)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..532.97 rows=28339 width=0)
                                       Index Cond: (pov = 1)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..785.58 rows=41754 width=0)
                                       Index Cond: (pov = 13)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..106.05 rows=5549 width=0)
                                       Index Cond: (pov = 216)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..292.88 rows=15526 width=0)
                                       Index Cond: (pov = 250)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..106.05 rows=5549 width=0)
                                       Index Cond: (pov = 124)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..106.05 rows=5549 width=0)
                                       Index Cond: (pov = 3)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..1071.77 rows=56979 width=0)
                                       Index Cond: (pov = 34)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..632.53 rows=33614 width=0)
                                       Index Cond: (pov = 235)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..360.01 rows=19144 width=0)
                                       Index Cond: (pov = 72)
                                 ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..106.05 rows=5549 width=0)
                                       Index Cond: (pov = 528)
                     ->  Hash  (cost=2015.70..2015.70 rows=518 width=122)
                           ->  Hash Join  (cost=473.47..2015.70 rows=518 width=122)
                                 Hash Cond: (gamelist.brandname = brandlist.id)
                                 ->  Bitmap Heap Scan on gamelist  (cost=262.19..1797.30 rows=518 width=81)
                                       Recheck Cond: (median >= 70)
                                       Filter: (((count2 >= 80) AND (sellday >= '2008-01-01'::date)) OR ((count2 >= 40) AND
(sellday >= (('now'::cstring)::date - '6 mons'::interval))))
                                       ->  Bitmap Index Scan on tokuten_index  (cost=0.00..262.06 rows=8237 width=0)
                                             Index Cond: (median >= 70)
                                 ->  Hash  (cost=152.79..152.79 rows=4679 width=49)
                                       ->  Seq Scan on brandlist  (cost=0.00..152.79 rows=4679 width=49)
(57 行)
pov1つ1つにBitmap Index Scan on povgroups_povが動いています。
->  BitmapOr  (cost=9403.99..9403.99 rows=408734 width=0)
  ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..344.66 rows=18164 width=0)
    Index Cond: (pov = 33)
  ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..391.88 rows=20726 width=0)
    Index Cond: (pov = 10)
以下略

一方、たくさんのPOVをINで指定した場合の実行計画は以下のとおりです。
ap2=# EXPLAIN SELECT '<img src="http://pics.dmm.co.jp/digital/pcgame/' || gamelist.dmm || '/' || gamelist.dmm || 'ps.jpg">' AS 画像 ,'' || gamelist.gamename || '' AS タイトル ,gamelist.sellday as 発売日 ,CASE WHEN brandlist.url IS NOT NULL THEN '' || brandlist.brandname || '' ELSE brandlist.brandname || ' (解散)' END AS ブランド ,gamelist.median as 中央値 ,gamelist.count2 as データ数 ,(CASE WHEN gamelist.dmm_subsc IS NOT NULL THEN '有' END) AS DMMプレミアム ,SUM(CASE WHEN povgroups.pov=33 THEN 1 ELSE 0 END) AS 萌ゲー ,SUM(CASE WHEN povgroups.pov=10 THEN 1 ELSE 0 END) AS コメディ ,SUM(CASE WHEN povgroups.pov=57 THEN 1 ELSE 0 END) AS シナリオいい ,SUM(CASE WHEN povgroups.pov=193 THEN 1 ELSE 0 END) AS 主人公強い ,SUM(CASE WHEN povgroups.pov=50 THEN 1 ELSE 0 END) AS ロリ ,SUM(CASE WHEN povgroups.pov=314 THEN 1 ELSE 0 END) AS 戦う女の子 ,SUM(CASE WHEN povgroups.pov=369 THEN 1 ELSE 0 END) AS 女装 ,SUM(CASE WHEN povgroups.pov=379 THEN 1 ELSE 0 END) AS 主人公モテモテ ,SUM(CASE WHEN povgroups.pov=1 THEN 1 ELSE 0 END) AS おかず ,SUM(CASE WHEN povgroups.pov=13 THEN 1 ELSE 0 END) AS 主人公素敵 ,SUM(CASE WHEN povgroups.pov=216 THEN 1 ELSE 0 END) AS アナルSEX ,SUM(CASE WHEN povgroups.pov=250 THEN 1 ELSE 0 END) AS 陵辱レイプ ,SUM(CASE WHEN povgroups.pov=124 THEN 1 ELSE 0 END) AS 女の子に襲 ,SUM(CASE WHEN povgroups.pov=3 THEN 1 ELSE 0 END) AS ゲーム性有 ,SUM(CASE WHEN povgroups.pov=34 THEN 1 ELSE 0 END) AS キャラ取巻く世界観 ,SUM(CASE WHEN povgroups.pov=235 THEN 1 ELSE 0 END) AS 奇人変人 ,SUM(CASE WHEN povgroups.pov=72 THEN 1 ELSE 0 END) AS 主人公ダメ ,SUM(CASE WHEN povgroups.pov=528 THEN 1 ELSE 0 END) AS 個別ルートダメ FROM (gamelist INNER JOIN brandlist ON gamelist.brandname = brandlist.id) INNER JOIN povgroups ON gamelist.ID=povgroups.game WHERE gamelist.median >= 70 AND ((gamelist.count2 >=80 AND gamelist.sellday >= '2008-01-01') OR (gamelist.count2 >=40 AND gamelist.sellday >= CURRENT_DATE - interval '6 month')) AND (povgroups.pov IN (33,10,57,193,50,314,369,379,1,13,216,250,124,3,34,235,72,528 )) GROUP BY gamelist.sellday,gamelist.count2,gamelist.median,gamelist.dmm,gamelist.id,brandlist.url,brandlist.brandname,gamelist.dmm_subsc ORDER BY gamelist.sellday DESC,gamelist.count2 DESC;
                                                                                    QUERY PLAN

----------------------------------------------------------------------------------------------------------------------------
-------------------------------------------------------
 Sort  (cost=54480.58..54502.87 rows=8918 width=355)
   Sort Key: gamelist.sellday DESC, gamelist.count2 DESC
   ->  HashAggregate  (cost=53471.84..53895.45 rows=8918 width=355)
         Group Key: gamelist.id, brandlist.url, brandlist.brandname
         ->  Hash Join  (cost=9425.55..52602.34 rows=8918 width=126)
               Hash Cond: (povgroups.game = gamelist.id)
               ->  Bitmap Heap Scan on povgroups  (cost=7403.37..48958.22 rows=408734 width=8)
                     Recheck Cond: (pov = ANY ('{33,10,57,193,50,314,369,379,1,13,216,250,124,3,34,235,72,528}'::integer[]))
                     ->  Bitmap Index Scan on povgroups_pov  (cost=0.00..7301.18 rows=408734 width=0)
                           Index Cond: (pov = ANY ('{33,10,57,193,50,314,369,379,1,13,216,250,124,3,34,235,72,528}'::integer
[]))
               ->  Hash  (cost=2015.70..2015.70 rows=518 width=122)
                     ->  Hash Join  (cost=473.47..2015.70 rows=518 width=122)
                           Hash Cond: (gamelist.brandname = brandlist.id)
                           ->  Bitmap Heap Scan on gamelist  (cost=262.19..1797.30 rows=518 width=81)
                                 Recheck Cond: (median >= 70)
                                 Filter: (((count2 >= 80) AND (sellday >= '2008-01-01'::date)) OR ((count2 >= 40) AND (selld
ay >= (('now'::cstring)::date - '6 mons'::interval))))
                                 ->  Bitmap Index Scan on tokuten_index  (cost=0.00..262.06 rows=8237 width=0)
                                       Index Cond: (median >= 70)
                           ->  Hash  (cost=152.79..152.79 rows=4679 width=49)
                                 ->  Seq Scan on brandlist  (cost=0.00..152.79 rows=4679 width=49)
(20 行)
->  Bitmap Index Scan on povgroups_pov  (cost=0.00..7301.18 rows=408734 width=0)
 Index Cond: (pov = ANY ('{33,10,57,193,50,314,369,379,1,13,216,250,124,3,34,235,72,528}'::integer[]))
と、一回のBitmap Index Scan on povgroups_pov でpovを探しています。

ORでつなぐよりINを使った方が速いです。