The Wii had three things behind it that made it the success that it was.

1) It was the first of its kind. People had to have it because it was something they'd never seen before.

2) It had exceptional marketing. I'm not sure a physical product can "go viral," but that's the only term I can think of to describe what it did. It went beyond simple advertising to become a cultural phenomenon, and that's something that's hard to replicate. In other words, it got lucky.

3) It was cheap. Wii offered next generation games (as far as the average consumer knew) for half the price of its competitors.

...Kinect won't have any of those things. It'll be viewed as an expensive "me-too" add-on.