according to this post (
http://forums.steampowered.com/forum...77&postcount=7) all versions of the game should be activatable on Steam so that everyone can buy DLC off Steam.
is there anybody here who's bought the game outside of Steam but managed to activate it on Steam? according to GetGames it didn't work earlier tonight, but it might have been due to the general mess on Steam concerning the CD keys for the game.