Marketing is the most important thing. Nintendo had a habit of releasing new DS models almost yearly, which conditioned people to believe a new DS would just be a continuation of the existing system. The 3DS just came off as a DS with 3D, like the XLvwas a DS with a bigger screen. If Nintendo showed people playing Wii Sports Resort 2 with Wii remotes, the confusion would be understandable, I think. WiiU will have HD, with a tablet controller, and games that looked substantially better than the Wii. The visual upgrade is the important part, because it's easy to show that it's an upgrade, not just a redesign.
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"When I was a young man, I had liberty, but I did not see it. I had time, but I did not know it."