It's simple math. When you add up all the votes in the states, you get the national vote. Well, I've done that, with the average October poll. When there was none, I made up a number that was in line with how much a state should move based on the national polls.
The result is Barack Obama leads by 0.81%. Wait, you say. The RCP average says that Mitt Romney is leading by 0.90%. How can they both be right? They can't. If the RCP state averages are right, then the national average is wrong. If the national average is right, then the state averages are off by an average of 1.71%. That means that Romney should be leading in any state where the RCP average is below Obama +1.5% and should be in at least some of the states where Obama leads by 2.5%. And there are four of those.
If you believe the national polls are close to accurate and they were within 0.3% of the 2008 margin, then the race in swing states is much closer than it appears.