One thing that the article implied but didn't seem to say outright: This is a CONSERVATIVE estimate, arguably a worst-case scenario. They need to estimate, for budgeting purposes and the like, how well it will sell.
Personally, I would love to get it, but I'm unable to at the moment (I've only gotten one game this year. Wouldn't change it, though.), and I know several friends that are attending the midnight launch and I definitely think it's this year's biggest title.
On the subject of FPSes and CoD as a whole: They're all screwed, at least at the way it's goign now. The complete dominance of the FPS has to end, or at least abate a little, soon, it can't just keep growing. Hopefully this will lead to innovation on the order of the original Halo or Half-Life. (I say give them better stories.. maybe competitive MP in the actual campaign?) CoD in particular is getting beaten into the ground, same as Guitar Hero. Look at what happened to IW!