Wii U already a problem child for developers
A "reliable source has indicated that the Wii U may be a headache for some developers, as "the final hardware has been 'rushed through the door'". Of all the consequences that one can expect from rushed hardware, the worst is when it won't work as advertised. That is exactly what claims are being brought up in regards to the Wii U.
Worst of which is the wireless functionality, which "simply do not work at all". In fact, even the tethered controller which "still does not work properly". Which begs the question, what is the point of a new controller if it doesn't work? The source of this rumor is 01.net and they conclude that developers are expecting Nintendo to release this hardware in June 2012. As the engineers work feverishly to make everything work.