They're not Sony, they know how to do this and know what works on one console doesn't on another and vice verse. The only time they fucked up was with the VirtualBoy which is neither handheld or a home console.
Nintendo 64, Gamecube. Because cartridges worked so well on a home console when both competitors used the CD, because a 4kb per-texture limit was a brilliant idea, because a complete lack of multimedia features in the advent of the DVD was a brilliant move, because using miniDVD-derrivative storage and restricting tbhe use of DVD and DVD-Video was a great idea.
Nintendo aren't gods - don't fool yourself. Every console does missteps sometimes.
Back to the subject though, the 3DS is a handheld, the WiiU is a home console - they're two different platforms, and in the area where the corresponding markets meet, the systems can co-exist.