Zurvan7: most of the DRM lies with the publishers and not with Valve.
That cop-out doesn't really work. Steam could just say no, just like GOG does. You know, having at least some principles (that favor the customers, not only the publisher or the store itself).
The very least, Valve could require from the publishers that all Steam games have only Steam-DRM, and no 3rd party DRM on top of it. So when Steam users complain that some Steam game had GFWL, or Tages/SecuROM with activation caps, they should also direct part of the blame to Valve
for allowing that shit in their own service.
Same goes to e.g. the region restrictions, selling only cut-down versions in Australia or Germany, etc. (in case you don't like them). You can't just always go behind "Oh the publisher wanted it, so there's no way we (Valve/Steam) could have said no.". Of course they could, if they had any principles to protect also the rights of the customers.