Just because N doesn't sell as many consoles as the competition doesn't make them unsuccessful. We've seen in recent quarterly reports that the Wii U is starting to make a profit. Their operating costs as a company are just far lower than MS and Sony. They don't need to sell as much to create that cash flow.
Nintendo's main competitive advantage is that they have games that can't be experienced anywhere else. If they go 3rd party, they have lost that.The fact that so many people want them to choose this route shows how powerful their IP are. Wii U may end up being a bust sales wise, but many people will come crawling back to Nintendo eventually because they will miss their great original content.
run away!