Yeah, the way I see it is that in addition to what I've said earlier in the thread, the casual crowd which was a huge segment of Wii users and helped make it such a huge success are likely comfortable staying with the Wii. Nintendo hasn't really given that crowd a good incentive to upgrade beyond HD and better graphics, so why would they upgrade, especially when they're things they very likely don't care about? And the added layer of complexity vs the simplicity of the Wii? Nintendo have themselves in an interesting dilemma, and that doesn't even count the price.
I think one of the main reasons for why the Wii doing so well was that it was priced just right. Anyone with curiosity would be able to pick one up, if they could find one on the shelves. I expect that people are balking at the price of the Wii U, leading to a less than enthusiastic adoption rate. I don't think anything can change now, but as I've said earlier in the thread, I think they could have made the pad optional, maybe a bundle with a game that requires it, which would have made it possible for the price to be more reasonable, but as it is, I think it's too tied to the system itself.