The Wii U isn't selling on eBay as the Wii was. Does that mean the Wii U is less popular? That's one way of looking at it. We could also guess that the system stock isn't anywhere near the dire situation that the Wii faced. Again, this could have to do with popularity or Nintendo learning from their mistakes. Whatever the cause, the effect is Wii Us selling for retail price on eBay, if they sell at all.
Feature here (thanks Jet Pilot!)