Actually, I think Jennings' use of the word "instinct" is appropriate. Apart from partisan columnists like Paul Krugman and Molly Ivins, who often deliberately mislead their readers, I think most liberal bias is not a matter of conscious bias and manipulation, but of "instinct," of reacting to certain themes that resonate in their personal mythology and worldview, and of disregarding or minimizing the importance of information which does not conform to those themes. Thus, Abu Ghraib is maximized because it conforms to the theme of "Republican-led wars are bad, Rumsfeld/Bush are sinister," etc., whereas oil-for-food is minimized because "the U.N. is corrupt and France was on the take" are not part of liberal mythology. It's not as if they are consciously thinking, "We like the U.N., so we will protect it by downplaying this story."
Steve: I think you are right. The distortion might be conscious for some in the media but for most, I believe, it is something that subconscious. Anytime the exercise of judgment is involved (think "editorial judgment" or newsworthy judgment), an individual's personal bias is going to affect his or her decision. The media's denial of this is what really bothers me.