Eurogamer has confirmed with Atari that the deal is for timed exclusivity on Sony platforms, with all other versions being released "later in the year." It's certainly a strange move on Atari's part, especially when limiting their potential consumer base is being called "maximizing the launch of the Ghostbusters videogame across Europe" by Atari's VP of Worldwide Marketing. Pushing non-Sony versions further towards or, even worse, into Q4 won't do the 360, Wii and DS versions any favors.
Update: Atari US has clarified its publishing plans for the North American region. The 360, PS3, Wii and DS versions will all be released in the US on June 16, as previously announced. The PSP version will be released worldwide in Autumn.