Diablo III requiring an always-online connection for PC is one of the worst design decisions in recent memory. Well, any single-player game that requires an always-online connection is asinine, really. It looks like that poor decision will not carry over into the PlayStation 3 and PlayStation 4 versions of the game -- at least not in local multiplayer.
In an interview with GameTrailers, Sony's John Hight said "You can have four people on the same screen. No split-screen, we just zoom the camera out. Or, you know, if you're offline..."
So there it is. It is unclear if the single-player game can be played offline since Mr. Hight was speaking specifically about multiplayer in this instance, but it wouldn't surprise me if it was. Congratulations, future PS3 and PS4 owners, you officially have a better version of the game.