I would like to have a box copy of Wasteland 2 for aesthetical reasons, but actually I prefer pure Steam in usage. So can I play Wasteland 2 with just a Steam with no disc, after initial installation?
Yes, they do. The game is published by Deep Silver / Koch Media from Germany and all of their recent games are Steamworks. Watch out for the publisher when buying in Russia or Asia though. Could be a different one.
Developer confirming this:
Also, the disc apparently does not include the game, but only the Steam Client: