Okay, now than you mention it, though, those buttons almost look Photoshopped on or something. They might have just wanted to enhance the shine a bit but got the button order mixed up in the process.
EDIT : yeah, the light is reflecting from a different angle on those 4 buttons and the home button in the center when compared to the reflections on the analog sticks.
EDIT2 : It's interesting, too, though, that when doing an image search I get at least 2 other models with the same button placement problem coming up in google.
The other two don't seem to be for Wii (one the image name says Android) but whoever was putting together the pictures might have just not been able to see the letters in the photo and enhanced it, drawing them on manually ... but had experience from other non-wii U models that got him confused.
EDIT3 : I now noticed that the non-Wii U Nyko controllers shown here actually have the X and Y positions switched, too, which basically gives them an XBox controller configuration. All the more reason why the photoshopper could have gotten confused from previous experience.