This is a title of a blog on Time.com. Apparently research by The Pew Research Center has shown that Obama does indeed receive more favorable coverage than McCain: 36% for Obama vs. 14% for McCain. The simple explanation--according to Pew--is that there is more positive news surrounding Obama's campaign.
I'll leave it to the experts to discuss the press coverage. Regardless who wins this election, the post-mortem will go on forever. I'm sure there will be a number of books written about this campaign.