The lack of offline play in Diablo 3 was a point of consternation at the game's release (and before, and since). So the news that the recently announced Playstation release of the game will feature an offline mode for local co-op is a tad surprising. Previously Blizzard stood by their choice arguing that always-online play was "critical for the long-term integrity of the game experience".
Blizzard have not yet confirmed the offline mode for Playstation but in the Gametrailer interview below Blizzard's vice president of creative development Chris Metzen and production director John Hight mention it in a discussion of local co-op.
WoW Insider over at Joystiq spotted that about the 8.35 mark that Hight says "we're going to allow for local co-op as well as online co-op. So you can have four people on the same screen, no split-screen, and we just zoom the camera out, or if you're offline..."
Frustratingly, Hight is cut off by Geoff Keighley so we don't hear if Hight was t go more into this offline mode. Hopefully there is a chance that if the feature were coming to consoles then it may also appear on PC.
We've reached out to Blizzard for a confirmation.