Your assuming the swing would have to be identical between states. Whereas recent polling shows Romney doing a lot better then McCain in Massachussets(40% Romney to 51% Obama), and that's leaving a substantial undecided vote. Assuming it splits slightly favourably to Romney, that's 45/55%. Which means he only needs an additional 5% swing over the course of this campaign.
Simple math folks.
Rasmussen has been showing better results for Republicans a lot of places, Obama certainly will be well over 50% on election day. Second, uniform swing I referring to is based on the previous presidential vote. With a big national swing, Romney would have to over-perform in a big way in Massachusetts to get 45% and he just doesn't have that sort of appeal in the state. 1-2% points from what McCain got may be possible, but beyond that, it's not going to be much different.