Looking at it from a strictly financial view: Even if Nintendo "loses" this generation - even if the Wii suddenly stops selling completely from now, Nintendo have most likely recouped their R&D and made money in this short time.
In other words, Nintendo cannot lose because they have already "won" back their initial investment. That alone speaks volumes especially when you pit Nintendo's financials against Sony's and Microsoft's.
And no, I don't know how much Nintendo have invested in R&D for the Wii, but it's safe to say they didn't spend nearly as much on R&D (compared to Sony and Microsoft on their respective consoles) as much as they did on marketing and strategy. I mean, how hard is it to add "low-cost waggle" to "outdated technology that amounts to nothing more than two gamecubes duct-taped together"?
