Last I heard the contract that Activision has with Microsoft and Xbox is that they recieve all map pack bundles for COD a month earlier than any other console.
I'd hazard a guess that this means that all PS3 and PC owners will get the maps on March 1st.
It's a bit of a bummer that Xbox had to go and buy out the rights and make everyone else suffer in their undies for an extra month, but it was purely a buisness decision.