Why buy short games?

As anyone who follows my blog regularly knows, I'm a fanatic about replayability when it comes to games. I don't buy games unless I think they'll last me more than a few weeks.

I can think of plenty of movies that I respect as good movies even though they're really only great once through. Two examples are The Game and Memento. But the films I buy on DVD are ones I know I'll want to watch again from time to time.

There are paintings that I can appreciate but wouldn't want to look at every day. Any poster or picture I buy to hang on a wall or set on a bookshelf is going to be one with continuous value. Scarily enough, one of my sister's gave me a card copy of that painting once because "it made me think of you" -- yeah, that should tell you something. =P

While people commonly make impulse purchases of music albums, I think almost everyone would say that he or she tries to buy only music that will last.

Is it different with games? I don't think so.

True, a 10-hour game will last a long time for a gamer who can only play 10 minutes here, 30 minutes there. But I think the only reason so many people choose to buy short games for $50, rather than rent them for $10, is because rental services keep such low stocks of each game. If a gamer could go to a rental store or online service with near-certainty that the game he wants will be in stock, what reason would there be to purchase the game instead?

If a gamer isn't sure how much playtime he'll be able to squeeze in on a given week, that doesn't necessarily mean he has to re-rent the game and pay more. Gamefly allows renters to keep a game as long as they continue to pay the subscription fee. Even if the renter took two full months to complete the game, the cost of both months' subscription is still less than buying a new game... and Gamefly allows two games out at a time.

What do you think? Is there any reason short games don't go straight to rental, like B-movies go straight to Blockbuster, other than rental stock shortages?