It was announced today that Xbox 360 version of Metal Gear Rising: Revengeance is not going to be released in Japan, but since that revelation, Konami has announced that the game will still be released over here as initially planned.
Speaking to MCV, a Konami spokesperson confirmed that the game's European launch would remain unaffected, and that there were "various reasons" why the Xbox version of the game was cancelled in Japan. It's probably safe to say that lack of demand was likely a key contributing factor in the decision, although nothing specific was mentioned by the publisher.