Seriously, that is what pisses me off the most about Blizzard's practices. They announce or let slip information about their games when they're not even past the conceptual stage, which makes everyone go HOT DAMN NEED THIS NOW for like the 10 years following the entire fucking development cycle of the game.
Hell, look at Warcraft Adventures and Starcraft Ghost, they got announced with fucking CONCEPTUAL ART AND VIDEOS, ended up being cancelled for being awful shit and people WOULD NOT SHUT THE FUCK UP about the game.

I still wonder what happened with that game, and why they waited like 5 years just to cancel it. I was so excited for starcraft ghost.
And IMO,
I think they will be making a diablo3. As unlikely as blizzard says its going to be, I dont see much reason in taking down the diablo3.com site without some indication that they are in the process of making it. I guarantee that in 1-2 years the diablo3 site will re-done with screen shots and info about the game. Oh well I'm actually excited, diablo was one of my favorite game series. I still love playing them every once in a while.
- However... as good as a new diablo 3 game would be. Idk about a prequel... I mean diablo,mephitso, and baal were always the fun parts of the game, being able to kill them... If it is actually going to be a prequel, you obviously wouldn't be fighting diablo... and if its after, they are already dead. So who will be the antagonist(s)?