Dzsono: I would be very interested to see the results of a bought/played survey.
For me it's only about 15% of all my games completed, but also only 13% of them never installed (the percentage of games never played might be a little higher, maybe around 20%, since some games I only installed to realize they don't work with my graphics card). And of course lots of games I "played" I just played for an hour or so to see what they're like and then postponed their continuation or even abandoned them if I didn't like them. And I'm playing too many games at the same time, always depending on what I'm in the mood for. :/
Anyway, I'm not sure it's just huge discount sales, although low prices certainly play their part. I think it's also the enormous supply and the tough competition in the market, combined with the games' easy accessability via digital distribution. It's easier as ever for developers to distribute their games, but it's near impossible to be
that game, the one and only that players will dedicate all their time to, because there are too many alternatives and few games really stand out.