I think he is wrong about advertiser pressure: I don't think advertisers care (much). I think it is that owning a media outlet is a way for rich people to have fun--and once you own it you want to play with it, and make sure that it reflects your not-terribly-informed and self-advancing view of the world:
Seeing the Forest: It comes from the top: From Glenn Greenwald:
JESSICA YELLIN, CNN CONGRESSIONAL CORRESPONDENT: I think the press corps dropped the ball at the beginning. When the lead-up to the war began, the press corps was under enormous pressure from corporate executives, frankly, to make sure that this was a war that was presented in a way that was consistent with the patriotic fever in the nation and the president's high approval ratings.
And my own experience at the White House was that, the higher the president's approval ratings, the more pressure I had from news executives -- and I was not at this network at the time -- but the more pressure I had from news executives to put on positive stories about the president....
[Media critics] tend to be too willing to slip into the "Heathers" or "Villagers" explanation. Supposedly the media are staffed by a bunch of silly, shallow, people who only talk to each other and who, for example, did what they did to sabotage Al Gore's Presidential run because he annoyed their silly little high school sensibilities.
I've always believed that it was a management problem.... This does not mean that the Heathers are not silly people.... [This] doesn't mean that they're not culpable. But the people whose names we see are quite literally hirelings and lackeys.... They give management what it wants.
Greenwald gives... a long list of reporters whose newspaper careers ended or dead-ended because of excessively accurate reporting -- Seymour Hersh is the most eminent of them.... All I claim is that management manages, and that reporters can be hired, fired, promoted, and demoted.... As for management's motives, I have no way of knowing that. My present guess is that the owners and managers of the big media favor war and low taxes (and the ending of the estate tax, which is a major factors for the few family-owned publications: see here) and are responsive to the normal kinds of favors that the federal government can hand out. They are not right wing on other issues, but the Bush administration really isn't either -- by now they've double-crossed most of their conservative ideological constituencies by now. (That is to say, nativists, cultural conservatives, fiscal conservatives, and above all little-government conservatives.)
I'm sure that organized winger pressure is a factor too, but public opinion isn't the reason: the big media have always been more hawkish and more anti-tax than public opinion. I much bigger factor is advertiser pressure...