That 5.2m is based on pure speculation. It almost certainly involves shipment figures (units MS sold are "shipped" units), and no one knows exactly how many units of Halo 2 or Halo 1 have been shipped either (WW).
That said, I wouldn't be surprised if 3.5m units have been sold WW to date. Most people (?) that want Halo 3 now have it??
Gesta Non Verba
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