From Blizzard Australia: (20/01/2011)

While working on Diablo III we’ve been called out for messing around with systems too much, that the game is good as-is and we should just release it. I think that’s a fair argument to make, but I also think it’s incorrect. Our job isn’t just to put out a game, it’s to release the next Diablo game. No one will remember if the game is late, only if it’s great. We trust in our ability to put out a great game, but we’re not quite there yet. In addition to finishing and polishing the content of the game we’re continuing to iterate on some of the core game systems. So all that said, I’d like to provide everyone an update on some of the systems we’re currently working on.