I don't know that any of those things are true. Nintendo is just as quick to put a franchise on the shelf as anyone if sales disappoint, and although this could be more about cost of opportunity than games not being profitable, I don't think Nintendo games are as cheap to develop as you seem to.
We also don't know that Nintendo can be profitable off a 20 million install base because they've always had successful handhelds to carry their unsuccessful consoles. And by following their own path it's true that Nintendo is sometimes less affected by "craziness" in the industry than other companies, but this has a trade off because it also means that they sometimes see their business decline even when the industry as a whole isn't declining.
So I'd expect Nintendo to be in the console business longer, but because they are only a video game company and not a corporation that dabbles in video games like the other two.