Duke Nukem Forever, Command and Conquer Tiberium Dawn, roughly speaking World of Warcraft, and that's just what I can think of off the top of my head. You just haven't been paying that much attention to what's upcoming compared to what's already out.
There's also the fact that it's Blizzard...barring attempting genocide they can do pretty much whatever they want if it thinks it'll make them money. For example, announcing a game such as Diablo 3 or SC2 get a lot of the internet buzzing about it, drawing attention from people who've not heard of them, and possibly making them try Blizzard's (excellent) games. So announcing games that early in advance indirectly increases their profits.