I have no idea what USA Today is thinking with this graphic. They seem to have taken all the polling data from 2008 for Obama vs. McCain and fit them to some arbitrary function. Never mind the convention bumps or that the lead has switched a few times, what they show is two lines with very little motion, from January to October. For a contrast, look at the supertracker at fivethirtyeight.com. There, the lines help you to see the motion in the polls, such as the sharp changes near the conventions. The USA Today lines simply make it harder to look at the graph.
What gets me about this, though, isn’t the ridiculously bad math at one of the nations top selling newspapers. It’s the caption that appears if you hover over the line for, say, Obama: