"Personaly, I don't want Steam"
Valve is using Steam also for fighting the cheaters.
Not just for updates and movies.
It was mentioned in one of the recent interviews.
Saying they will update/change the codebase, possibly daily, to render any hacks useless. With steam running on everyones computer if they release a patch everyone is immediately up to date.
If it really works to keep out cheats that would be very cool imho.