I believe the publisher fell through, so they had to find another publisher.I've been anticipating this game for a long time; I can't wait for next week!
Wasn't it initially supposed to be released a few months ago?
It was supposed to come out last fall (October, I believe), but as Activision moved through its merger with Vivendi, its management chose to drop pretty much every Vivendi game in development that the company couldn't sequelize to hell and back. Brütal Legend, Ghostbusters, Chronicles of Riddick, and a few others were subsequently dropped into publishing hell, until Sierra was able to convince Atari to publish Ghostbusters.
Another importer that I've seen come highly recommended is Video Games Plus, which is based in Canada and currently offering the Xbox 360 version of the game for $69.99 ... so, £39 or so?