Interesting analysis. I think it's likely the Wii will manage to break the 50 million barrier.
I seem to recall being brazen enough to claim the Wii might top 200 million worldwide by the end of this gen, way back in like 2007. That's now looking nearly impossible. Of course, at the time I had also assumed this gen would be unusually long, not ending until 2013-2014. That's looking less and less likely as well.
I'm still hoping we'll be able to top 300 million total consoles sold by the end of this generation, but at this point I wouldn't bet on it. I think my original estimation way long ago was 250-300 or something.