DRM is the games publishers' choice, no matter what distribution platform they use.
Steam doesn't force DRM on publishers and there are plenty of games there without DRM.
There is also already plenty of DRM-encumbered Linux software (I'm thinking of electronic engineering vendors, but that's only because my field of experience has led me there). If Steam will do anything in this space, it will bring mainstream visibility to the potential of software licensing mechanics in Linux.
