Ghostbusters now being a timed exclusive to PS3/PS2 during the movie's release (at least in EU) would lead to less sales on the Xbox version potentially. It'll get pushed into Christmas season and may get drowned out while the PS3/PS2 version is selling along with the movie. I imagine the movie is hitting the same demographic in terms of age as PS3 owners too.
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Just the sort of thing the Europeans are used to I guess.