I was watching a "Caught on Camera" show this weekend about the worst courtroom incidents -- shootouts, stabbings, etc. Really horrible stuff. And I thought, "Wow, the world is pretty bad and crazy and humans can be really awful."
Then, on my way to work, I was driving through the suburbs, listening to some goofy morning show and thinking, "Hm. The world is pretty good and mundane and human beings are mostly really cool. That show made me believe something worse than reality."
The truth, of course, exists, where the world is exactly x% good and human beings behave at exactly x% coolness, regardless of how I feel about it after being exposed to some crazy badness on TV, or some normalcy during my commute.
In your examples, you seem to have something simlar: Sensational account of violence vs. a blog saying that the media picks stories they think are sensational.
I think it is probably a good heuristic to think to yourself "Calm down. They get paid to show interesting and scary stuff even if, and maybe expressly because, it is super rare" while watching the news. But I don't see any data here to conclude anything about the "knockout game".
When I started seeing stories about the "knockout game" (supposedly, teenagers playing a game where they try to knockout random strangers) a few days ago, I immediately resolved to avoid paying attention to them, because it sounded like a classic case of people taking a few isolated incidents and blowing them up into a big scary trend.
And then this morning, I see this blog post, which links back to an article from two years ago titled: "Knockout King: Kids call it a game. Academics call it a bogus trend. Cops call it murder." Turns out my knowledge of human biases has served me well... and it's especially significant that the article is from two years ago; this is not the first time the media has tried to get people scared about this "trend." From the article (emphasis added):