I just went back and looked up Wii launch figures--apparently it sold roughly 600k in the first eight days in the US? If we accept that Nntendo was really producing Wiis at capacity (and I think the "faking it for attention" argument for the Wii did eventually die off), and Gamestop's allocation really was 100k consoles, I don't think Nntendo is grossly lowballing launch shipments to create hype.
Do we know if the 20/store or 100k chain-wide guess numbers are supposed to be model-specific? Assuming it's both versions combined, that's still 1/6th of the Wii launch total allocated to just GameStop. If that's per-model, it bumps up to a third.