Looks like with Steam they require to be online while you play, even for single player mode. I don't like that, myself. Wonder if the boxed version will have the same DRM, or worse....
The text of the DRM is located on the right, on the bottom of the game details. Well, at least it doesn't have minimum installs. But what happens if my DSL goes down, while playing? Which does happen from time to time....
http://store.steampowered.com/app/901248/