Capcom's Japanese site for Lost Planet 2 has been updated with estimated release periods for both the Xbox 360 and newly-announced PlayStation 3 versions. The Xbox 360 version is listed as coming out this winter, but the PlayStation 3 version has an undetermined date. It appears, then, that Lost Planet 2 will be a timed exclusive for the 360, at least in Japan. Unless Capcom's unnanounced PS3 release window turns out the same as the 360 release window.
Unofficial sources (by which we mean gamestop.com) show the same North American release date, February 23, for both versions, but that could be a placeholder. We're currently inquiring with both Capcom and Microsoft to determine the timing of the North American releases.
We're more apt to believe, by the way, that the delay in Japan is due to starting the PS3 version later, and not due to any agreements -- because why on earth would Capcom agree to make something Xbox 360 exclusive in Japan for any period of time?
Update: Capcom has confirmed plans for a simultaneous PS3/360 release of Lost Planet 2. Read all about it here.