Having not had the time nor the constitution to slog through 40 or so more comments on this issue, I'll just say this and hope no one has mentioned it:
For anyone who has researched Japanese management philosophy, this decision is extremely unsurprising. (My background in this is a few graduate courses on Lean Manufacturing and the Toyota management system, which included case studies of many other Japanese and American companies following Toyota's lead. I'm by no means an expert.)
Japanese culture, and management by extension, is extremely different in focus from that of America. All too often in America (my country), major layoffs are seen as a way to bolster short term stock growth, because of the increase in cash flow it provides. (You're not paying people anymore, but your products are still being sold.) Where this strategy falls down is long term development. You just lost a percentage of your workers, so new products and new sales stagnate. Japanese management recognizes this, and has an increase focus on both the companies value to society (both to it's worker base and society at large.) So, they generally eschew short term "quick-fixes" to their financials in order to work through their issues and set things up for the future.
At present the 3DS business is very successful. That can float the company for some time, as it has been doing. Even though Nintendo has sold a very small number of Wii Us up to this point, that's going to change. The Wii Us that have already been sold don't disappear because sales numbers are slow, so you'll see a steady rise of the number of Wii Us in the wild as more and more Nintendo quaility software comes out. They've already mentioned that Pikmin 3 moved consoles, though not as many as they would have liked. As more and more of these quality exclusives come out, more and more people will see their desires for a Wii U rise. I myself have been moved from complete indifference to being on the fence about it by Pikmin 3. Another quality game and I'll see myself dropping $400 on the console and a couple of games easily.
In contrast, letting these first party games out to other consoles would be the death-knell for the Wii U. Who, of ANYONE, would buy one if you could get Pikmin or Mario or Zelda or Metroid for another console? The second screen confers nice advantages, but with Microsoft and Sony planning to extend their consoles onto smartphones and other devices, that advantage will be a thing of the past. The XBone and Ps4 are coming out _this year_ after all. That would leave Nintendo in a place where no one would have their console, still, and would therefore have no market for any exclusive software they would want to develop. Wii U sales might be moving slowly, but I'm willing to bet on the tortoise in this race.