Kinect sells itself I think, it has a certain je na sais qua (sp?) that people are drawn too.
I turned on Kinect at thanksgiving to give my nieces and nephews something to do and ended up being what the entire family did/watched all night. Even those that were not interested in actually playing, were interested in watching those that were.
I know that Kinect sold two more 360's that day, and I honestly am not some kind of Microsoft shill. In fact, I never brought up the suggestion that they should buy one for thier kids, my brother-in-laws approached ME for information on what they needed.
When people play it, they have fun and that is what video games are all about.
That's a long-winded way of saying I'm not surprised that Kinect is doing so well, and I AM interested to see what Microsoft has planned for the near term future as all these new adopters start coming on board.