Though only in so far as to requiring you to install it through steam.
I have physical media for some of my games that are "steam" connected. I cannot lend these to another person, nor give them to another even in my own household because they are locked to my account in Steam.
I cannot play some of my Steam, actually I think I only have one that will play, without first connecting to Steam.
So if Gabe wants to sell us on a brave new world perhaps he should free the games Steam holds hostage now.
Outdated list of DRM-free (once installed) Steam games: http://www.gog.com/forum/general/list_of_drmfree_games_on_st...
Installing the game requires both the steam client and a connection, this is authorizing the install and is DRM.