I think you're seeing competition in action. Before the Internet, there were 3 major broadcasting companies (4 after FOX gathered steam in the 80s) and one major newspaper per metro area. Ensuring the media's silence was as simple as making sure that all of the heads of these organizations knew that if they published, they would be the one organization that was shut out of all future news from the government.

Now, if the major news organizations don't publish something newsworthy but inconvenient for powerful people, they can be sure that it's going to show up on Twitter, or Facebook, or Wikileaks, or Reddit, or Breitbart, or HuffPo, or Gawker, or Hacker News, or somewhere. And if it's outrageous enough, it'll spread virally and the consequence will be that the media companies that missed it will look stupid, not that the information won't get out there.