During the Leipzig Gaming Conference, Tom Chilton, lead designer for the upcoming Wrath of the Lich King expansion said that since regular, small updates to World of Warcraft's graphics have kept the game looking fresh, and he sees no reason for a complete graphics overhaul. "For us usability is a lot more important," said Chilton. "We want to make sure that our game runs very well on low system specs. We want to make sure that our engine supports our stylized look. So for us it's really more that kind of iterative improvement works a little bit better for us."
While discussing the possibility of regular yearly expansions for World of Warcraft, Chilton said it is a possibility, but the way they develop them internally isn't set up for that kind of schedule. Blizzard usually sits down to focus on what features would make a great expansion, and then just moves forward from there.
Oh Blizzard, it must be nice to have such recognition and respect that you don't have to work under any time constraints at all. Looks like you made it.