I am re-reading Fear and Loathing: On the Campaing Trail '72, and ran across the following that I think explains media "bias" better than anything else, and actually fits the Occam's Razor principle since it is the most obvious/easiest explanation :
"This was one of the traditional barriers I tried to ignore when I moved to Washington and began covering the '72 presidential campaign. As far as I was concerned, there was no such thing as 'off the record.' The most consistent and ultimately damaging failure of political journalism in America has its roots in the clubby/cocktail personal relationships that inevitably develop between politicians and journalists -- in Washington or anywhere else where they meet on a day-to-day basis. When professional antagonists become after hours drinking buddies, they are not likely to turn each other in . . . especially for 'minor infranctions' of rules that neither side takes seriously; and on the rare occasions when Minor infractions suddenly become Major, there is panic on both ends.
A classic example of this syndrome was the disastrous 'Eagleton Affair.' Half of the policital journalists in St. Louis and at least a dozen in the Washington press corps knew Eagleton was a serious boozer with a history of mental breakdowns -- but none of them had ever written about it, and the few who were known to have mentioned it privately clammed up 1000 percent when McGovern's harried staffers began making inquiries on that fateful Thursday afternoon in Miami. Any Washington political reporter who blows a Senator's chance for the vice-presidency might as well start looking for another beat to cover -- because his name will be instant Mud on Capitol Hill."
I'd say plus ca change, plus c'est la meme chose - except, there's one problem with the idea that this is simply the rules of the game. They weren't the rules during the Carter administration, the Clinton administration, or the Gore presidential campaign.