Final Fantasy XIII may come out in 2008, it might not. Either way there was no promise from Tetsuya Nomura or statement from Square-Enix guaranteeing a 2008 release date for Final Fantasy XIII. Square Enix USA comments on the matter are as follows:
Although information regarding the release date of FINAL FANTASY XIII has been reported by certain videogame websites, Square Enix itself has yet to make an official statement on this topic. Any reports of a confirmed release date are erroneous and should be disregarded.
Square Enix will make an official announcement in the future concerning the release date when it has been determined.
Good things come to those who wait. Right now I’m waiting to see a playable demo before hearing a release date. Perhaps, Square-Enix will have a build of Final Fantasy XIII (any installment) at E3 or TGS 2008.