It's hard to believe that anyone who takes himself seriously as a journalist really sets out to reveal patent bias. Instead, it slips out in assumptions and attitudes.
Take the misstating of Governor Palin's quote about the Iraq war (I discussed it here). Charlie Gibson didn't deliberately chop it up and misstate it. Instead, he got the quote (probably from some producer), and it raised no alarm bells because he's simply unfamiliar with the way that regular Americans -- like Governor Palin -- think.
Suppose he had gotten something similarly "edgy" about Barack Obama. Chances are, he would have checked it out because it didn't "sound right" to him. That's because he understands Barack and Barack's coastal, Ivy League elite world view in a way that he simply doesn't understand Governor Palin's.
That's the insidiousness of media bias. It doesn't have to be deliberate to be real. But sadly for the press, the American people have caught on.