I heavily doubt that torrented games just lurking on someone's hd. They can be played briefly but for sure when someones downloads a games *will* try i out eventually. Take a look at comments over tpb and other torrent search engines; 90% of the leechers want to play almost any game over internet multiplayer. This actually means that they will invest time on the game itself. Moreover, I took a look last weekend to some very specific game's genre like offline beat 'em up and to my amazement I saw over 1.000 seeders on budget/mostly unknown new games. This is a huge loss for any small company (1000 users x 10 euro = 10.000 euros). OTOH, it seems Skidrow is alive and kicking, lol. Personally, I believe that new games have pretty high pricing level but are deteriorating faster than a decade of fifteen years ago. Perhaps the new medium of online downloading via developer's sites or steam - like services must have a role also.
As for an amiga app store, I believe it is impossible because we do not have the huge collection we did in the nineties.