The last game of the series has hit 4M LTD numbers overall, so is there any reason not to think that the next game won't do even better? Its designed to be even more accessible than the previous game, they said that even their 6 year olds had fun playing the game and the video/painting features indicate that the community will be even stronger than ever. Obviously the visual improvements would play a part too, but they are really just cosmetic and I doubt that they alone will be a significant factor in the success of the game. I don't doubt there will be bundling, but the overall userbase of the console will be cracking 40M at or soon after the end of this year and more people will be able to enjoy the game than ever before.
Tease.