The thing a lot of Nintendo fans here don't get is that the Wii really was a fluke, it was the right product at the right time and is extremely difficult to reproduce, see the PS1 and PS2 > PS3. Nintendo had been in decline in console sales leading up to it, the fans weren't enough to keep it competitive. The casuals were the reason they went from 20m the console before to 100m with this one. The Wii hit at just the right time with technology and a gimmick that brought in people who didn't grow up with gaming. The thing is casuals by their name and nature are not going to be repeat customers. They bought it, got the big games, maybe a Mario title, a couple simple motion based games and then that was it they had their fix. Most of them probably haven't touched it in years, at least people I know, it's either in a closet or they sold it because they never used it. Hence the flood of Wii's on the secondary market. It's doubtful that they will reinvest more than the original Wii in price to get a new console and another 50 for the game.
Nintendo surely converted some of those casuals into more reliable customers but the Wii U is not the big motion based gaming console that the Wii was, at this point anybody that wants motion gaming will probably have gone with Kinect now anyway or will be getting the XB1 in a couple months considering it's coming out before Wii Fit U. Also the lack of advertising by Nintendo is amazing, I never see anything on TV at least in the States and I watch channels that advertise the competition all the time. Casuals aren't on here or other gaming sites and unless they walk into the gaming aisle of their store, will probably not even realize what's out there.