Wii U will sell more because
A. Gaming industry has laregly grown
B. Nintendo's recognition has largely grown
C. It would take more than an 80% drop off from the Wii for it to sell less than GameCube, which has NEVER happened in the gaming industry (Other than maybe a few atari's)
XBOX ONE/Wii U/3DS/PC
RIP Iwata 12/6/1959-7/11/2015
Thanks for all the great memories!