I honestly have heard nothing of the sort, but I guess I'll see and find out

Yes, about the gamepad

The main reason why the N64 didn't sell better in Japan would be its software droughts. There were literally months without games. Momentum will inevitably collapse during periods of time with no compelling games at all.

The GC sold worse than the N64 (4m vs. 5m) despite a smaller controller. While the GC had more games than the N64, it was the successor to a console that wasn't the go-to place for home console games (speaking of the N64 here, obviously). On the other hand, the N64 was the successor to the SNES, a dominant home console. In other words, the general perception of Nintendo consoles had changed for the worse by the time the GC launched, so people were more inclined to choose PlayStation over Nintendo than a generation earlier when Sony was an entrant to the market.

The Wii wasn't locked within this perception, because its mission was to appeal to a broader market, not just the already established one. So the Wii did very well until software droughts began to occur again in the later years (third parties didn't like the system at all). The lack of space in Japanese homes is a myth, because Wii Sports and Wii Fit are among the best-selling games of all time in Japan. The Wii sold more than 12m units in Japan which is more than the PS3 achieved (which was flooded with high profile games).

The Wii U is failing for two main reasons. Firstly, its software droughts (it doesn't and won't get third party games). Secondly, it headed in the wrong direction. What made the Wii a success was for the most part deliberately removed. Ease of use and accessibility are gone with the Gamepad. Its not the size of the Gamepad that is the problem; the Pro Controller in its place would lead to failure too. All this creates a different image for the console (in comparison to the Wii). It doesn't help that the few software titles Nintendo put out so far are often similar to GC games (the GC was a failure, after all). Particularly the recent batch (Pikmin 3, The Wonderful 101, The Wind Waker HD) would be right at home on the GC.

America is a different matter, because multiconsole ownership is much more widespread than anywhere else. This means a console doesn't have to be the #1 choice in order to become a (modest) success in the region.