People have mentioned several times in this thread the prices for games, which is something I hadn't taken into consideration (even though it's fairly obvious). I never pay full price for a game. The most I've ever paid for a game is $20. Almost everything I own was $5 or less.
If I buy a movie ticket for $8, I stay through the whole movie, even if it sucks. I've only ever walked out of one movie. But if I rent a movie for $1-$3, I have no problem fast-forwarding boring parts or even quitting partway through.
I'll bet this does have a lot to do with my not finishing habit.