One factor in this could be that the only thing worth anyting in the "Hardened" edition is the original Call of Duty on Xbox Live Arcade, which of course we all own and is pointless for us.
With that missing the worth of all the special editions would be thrown off, and they would have to find some kind of replacement...
That said, they could just lower the prices $10 for everything and call it even.
Speaking of prices, the REAL issue with CoD6 is that they are so-far charging $60 for the PC version, the first ever time this has happened, and it could set a precedent.