Depends to whom they are selling it. There's approximately around 85 million Wiis in the world, mine being one of them. I still like quite few Wii games and play them occasionally, especially as party games like Rayman Raving Rabbits it's great choice. Wii U gives me possibility to update the Wii to powerful enough to get XB360 and PS3 level games later on, without need of giving up Wii compability and filling up our full stacked TV platform with another console. I do like the idea and I think I am not alone. Besides, you can get the Wii U from the shops end of this month (here.) and MS / Sony is nowehere near to seen, Nintendo can easily sell quite few of these before the competition ramps up for next generation.
Not that many of Wii owners are console-literate enough to wait at least half a year to see competition. They have not been interested about anything console-related before finding Wii and so it's obvious choice to them buy newer console that can run their old games as well.
Wii sold a lot to target audiences who never thought buying consoles, even less they are interested polygons or if the output is p-something. They just want to have a good time sometimes. So there's a lot fresh new ground to build up selling another generation.
