Well we were talking about entertainment
I did notice that at a point the coverage on McCain became more negative. It was shortly after McCain's campaign went mainly negative while Obama's remained mostly positive. Coincidence?
I strongly beleive that if he stayed positive there would have been more good things to say about him.
Let's give this situation:
"Obama today said he promises to do X and Y"
"Today McCain accused Obama of being X and Y"
You could report those as straightforward as you like, the second one naturally sounds more negative. It also didn't help that for a while McCain was harping on the same old points (this climaxed in the debates where at one point McCain responded 3 or 4 times in a row with different wordings of "he's gonna raise taxes!"), this didn't make for fresh news so Obama got more coverage.