Here it is in a nutshell:
A horse race draws attention and media outlets needed that with a boring and complacent drone that is Mitt Romney. With that said, the national polls are close and tight. The issue is the US President doesn't face a national election. in fact he faces 50 state-level elections that are aggregated to total. Those polls are not "close" in the sense that the president doesn't have enough states to gather 270 electoral voters. Yet, he is not ahead by overwhelming margins in many states. The movement of 3% of voters in 5-7 states, can change the election dramatically. So, in sum, it's not "nearly tied" but it's not a landslide either.