Originally Posted by qubit
AFAIK only Ubisoft implements this - for now.
Thing is, all the disc-based games have some form of intrusive DRM like securom or similar. Steam's DRM is account based and doesn't infect your PC with anything.
Steam's DRM is actually the kindest out there and there's a lot of benefits to having a Steam account, such as auto game updates, social functions, cloud-based games saves, easy installation of your games and you play them on any machine without hassle.
My gaming rig's never connected to the net (I have no interest in multi-player games) so no Steam for me. That means I will be most definitely boycotting any company that requires you to stay conncted to the net just to play a single-player game.