The top and bottom of the problem is (stating the obvious here) this :
Iwata absolutely NAILED it for Wii and DS - they identified a huge untapped area of gaming. One that wasn't interested in graphic fidelity, a forgotten much older area of gamers, female gamers etc. They did a pre-Wii/DS launch presentation at TGS and , with a bunch of boring graphs etc, pointed out exactly who they could scoop up, a rough outlay of how they'd do it, and then they -executed- to perfection. No mistakes - the Wii is a -masterclass- in marketting, effectively taking a dogproduct, rebranding it, adding a controller and making it into one of the hottest products in YEARS.
The problem is that that self same group of people Nintendo pulled in are now knee deep in a newer, more immediate "gaming" distraction : phone/mobile/facebook/web gaming. Low cost, low commit, secondary function to a required and commonly used item. The Wii was fun for what it was, but the software buy in was limited - that's going to hang heavy when people think about the Wii U (name/market issues aside) especially if the completely insane rumoured price turns out to be true.
Another problem that Nintendo have is that they need new gimmicks to pull in the crowds. 3DS is doing okay but on the back of being the budget/established choice in Japan and that's about it. The Wii U has very little that anyone outside of hardcore nintendo fans would give a twopenny fuck about. Infact, the whole approach seems to be for both 3DS and Wii U : Well, this worked last time - lets just try it again but this time with a new gimmick. The problem is that neither the touch pad nor 3D offer anything that a wider group gives a shit about.
That's not to say that both machines can't be successful on the back of big new ideas but repeating the trick seems to be one turn beyond Iwata and co. and their ill advised responses (Iwata saying that the slump in Nintendo's stock price is because stockholders fail to understand why the Wii U is so great is hugely laughable - especially as this is the second time he's pulled this) are not inspiring any confidence in the new platform and give away that they might be unprepared for what they are walking into.
All bravado aside, i'm not particularly Nintendo adverse - at the moment i just fail to see what the Wii U brings to -anyone- and the 3DS is the weirdest market leader i've ever seen : i like the machines ideas, but the hardware is largely awful and the software line up seems to be largely middling.