I dunno, honestly I think that it fights pirates, and its not like the games available on Steam are crap. If you buy a silver or above account, you get alot of bang for your buck (source games, all old games like original day of defeat
)
I have an old account at the moment, i have no qualms when it comes time to fish out 50 bucks and cry as 2 meg worth of my RAM is taken up by Steam :P
I feel kinda good that for once, i've forked out money for a game, and there arent people who have stolen a cd key for a free ride.. or my cd key for that matter.