The Wii was a raging success no matter how you look at it. Nintendo must be rolling in cash. Unlike Sony and MS, Nin was the only company to make profits on every console sold. MS and Sony got there eventually, but really, both of those companies aren't really gaming companies. MS is, of course, mostly a software company while Sony has it's hands in all kinds of business - apparently they make most of their money from Insurance.
Therefore, MS and Sony I think are in the business not so much for money (though that is important) but for advertisement, basically. Advertise their name, their brand. Familiarity breeds trust.
Nintendo, though? I'm pretty sure they are a gaming company first and foremost, so they can't drop out. They drop out, that means they went bankrupt. So Nintendo is most likely to fight tooth and nail to stay in the biz.