There are currently two principal dedicated handheld gaming platforms: the PSP Vita and the 3DS. Setting aside phones and tablets, that means the 3DS's only competition is the Vita. According to Wikipedia, as of June 30, 2012, the Vita sold a total of 2.2 million units. The 3DS had by that time sold 19 million units. That's not competition. That's pretty much monopoly.
The Wii was a misstep for Nintendo in the same way the iPhone was a misstep for Apple. In that it was, you know, the opposite of a misstep. The downside of Apple's iPhone was that it ruined Apple's image of being an elite company. The upside was...it became the second-largest company in America, and Microsoft could go suck it.
Now the Wii U...is clearly a failure. I'm fairly confident sales will pick up and it'll recoup its costs at least, but it won't match the other two consoles. It's tempting to point out, though, that it has, so far as I can tell, still outsold the Vita, even though handhelds traditionally outsell consoles.
NINTENDO: Even when we suck, somebody else always sucks more. (TM)