Good point. But isn't that how Silver "correctly projected the outcome" in all 50 states, by adding the expected value? The model showed Obama winning something like 318.5 electoral votes, but 332 if you added up ever state in which he had a >50% chance.
IIRC, Nate Silver discussed how his model does not treat each election as an independent event, but rather one party winning a specific race affects the probabilities of all the other races going a certain way (in that wining party's favor, of course). I forgot a lot of stats stuff since college, so this is begging for an SPC post to get into the statistical nitty-gritty.
