Can't say I'm surprised at overall sales coming off holiday. The Wii U is back where it was prior to holiday and bundle drops and I can't say I'm surprised about that either. The next major release in Japan is Donkey Kong Country TF, correct? I don't even think it will get much of a boost in sales off of that.
On the basis that the one genre they've got pretty well covered on the Wii U is platformers, I imagine you're probably right.
I've been wrong about this kind of thing before, but I don't imagine a huge upswing for Donkey Kong after 2D Mario and 3D Mario were already on the system recently and not much else has changed since the last one released a couple months ago.