It seems you cant pre order Modern warfare 2 on the Playstation 3, but you can for the PC and Xbox 360:
http://www.gamestop.com/browse/ProductMerch.aspx?groupid=445
Is it even remotely possible that Microsoft has aquired modern warfare 2 as an Xbox 360 console exclusive? Now this may be a long shot considering its gamestop, but then again it is something to keep watch