Eh. I think the problems with news media run much, much deeper than that.
Looking at the three main cable players, just because I love picking on them, and it doesn't take a lot of effort:
1. Fox has obviously always been nothing more than a right-wing propaganda machine, although they sometimes give voice to someone with at least some credibility (Shep Smith, Chris Wallace). They don't just poorly filter sources. They filter facts and events. They make a regular habit of selectively presenting information in order to paint a picture they know to not be accurate in order to tell a particular narrative. They have always done this. Standard Fox Headline: "Officer shoots violent attacker in self-defense; black residents in Ferguson loot and burn in response."
2. MSNBC has always been suspected of/known for having a liberal bias, although they, like Fox in the early days, peppered a few opposing viewpoints into their news salad here and there. I think they tried to report news for a while, until they realized they sucked at it, and Fox was making all of the money, so they dropped all pretense and are now pretty much the leftist Fox, keeping around Joe "Token" Scarborough for whatever reason. Like Fox, they heavily filter not only sources but events and facts, although they aren't exactly the same. If Fox is a propaganda machine, MSNBC is more like a coffeehouse of liberal elitists raging at each other and feeling superior in front of a camera. This is why they don't usually take the lead, instead spending most of their time acting as sort of a Fox watchdog. If Fox gets a story, you can bet MSNBC will have it exactly 20 minutes later, and it will come off entirely differently. I bet you won't find a roomful of people who watch Fox News more religiously than the producers at MSNBC. Standard MSNBC Headline: "Peaceful citizens protest the cold-blooded killing of unarmed black teenager by white police officer in Ferguson."
3. CNN is just an entirely different kind of strange animal. I think they still truly believe in the old-fashioned model of journalism, despite the fact that all of recent history tells us it is entirely unsuited for the modern cable world. In response to the difficulty of adhering to this old school journalistic model, instead of changing with the times, CNN has become so obsessed with the process, they lose sight of the actual act of reporting (Jon Stewart did a funny, if superficial, bit about this with the Selma bridge; this is something that goes way, way deeper down that just gadgets). They obviously know what Fox and MSNBC are doing, because they are clearly very concerned with making sure we all know they aren't doing those things. I bet if you watched CNN for 24 hours and added up the number of times someone said "We here at CNN" or something similar, it would far out-pace the same counts from MSNBC and Fox combined. They also seem to have this strange fetish with creating sensationalism that often manifests itself as absurdity (see: Don Lemon interviewing some random KKK guy). Standard CNN Headline: "Look! We have a reporter in Ferguson and we are talking to him right now, here on CNN, live, in real-time! And Ferguson is a BIG DEAL. So that's why we are here. CNN! Go team!"
All three are completely worthless, for a variety of reasons. I'm not saying your distinction between event- and source-filtering is wrong, or not useful. It is useful, especially with certain news sources that engage in genuine journalism, like the NYT, WaPo, WSJ, FT and Economist, to name my five favorite general news media. And on cable, probably BBCA and AJA, as well. But some news sources, including the Big Three cable networks, and the subject of the OP, NY Post, are so far lost, that the problems run much, much deeper than just filtering sources. Any reasonable media consumer that gets information from one of the Big Three, or from the NY Post, or a number of other sources, should automatically default to the position that it is probably worthless information, until they see something that suggests otherwise.
goat