I disagree. Even though the polls in September were skewed +D, it still was a tie at best. People defaulted to Obama until they knew that the challenger was someone capable. They probably just defaulted their choice until a credible choice presented itself. That first debate was the catalyst, and the preference cascade has started. People are jumping off the Obama bandwagon now, as they see that it is ok to do so.
That was essentially the same dynamic in 1980. Voters really wanted to dump Carter; but until Reagan destroyed the myth that he was a right-wing crazy they weren't ready for him. The contrast is nearly as stark now: Romney is no Reagan, but 0bama is Carter on steroids.