Blizzard are not a studio known for their love of innovation. What they do is perfection. They are probably the richest game developers in the world atm and yet they have what, 4 titles... they keep remaking them and polishing them. I like their style, even though they've turned into huge corporate whores with WoW.
There will be changes in Diablo, just not major ones. And TBH, i think it's better, major changes never work with cult-level games.