It wasn't supposed to be in Vancouver again (originally). The plan was originally to have Ottawa host this year but due to their slow stadium construction they decided to move it to Vancouver.
http://en.wikipedia.org/wiki/102nd_Grey_Cup
EDIT: This really didn't answer your question at all, just thought it was an interesting tidbit. I think You Need a Thneed brings up some great points as to why the Grey Cup is scheduled in advance