And these corporations are mostly run by liberal elitists like Viacom/CBS's Sumner Redstone. Memos from the boss are wonderful things. Bernard Goldberg wrote a very good book, Bias, on his experiences at CBS News, and their institutional bias resembles that at CNN, MSNBC, NBC News (where the liberal bigot Brian Williams is boss and anchor), etc, except Fox News.
Try actually watching news programs and pay attention to which networks report which stories and how they do it. That's how the rest of us learned that there is definitely a liberal bias in the national media.
And there's a reason for that - in journalism class in college, there are fewer "hard questions" than in the physical sciences or other tracks toward a professional education. Truth is relative in J-School (I minored in Journalism and was a radio announcer and editorial cartoonist for the student newspaper in college). So bias doesn't so much creep in as own journalists from the get-go. And that bias is predominantly liberal.
Nacho, I own a copy of Liberal Fascism, I agree with Goldberg's conclusions and your assessment of it.