This has been going on for a long time. For example, the Los Angeles Times bloggers were asked not to blog about the John Edwards' affair by Tony Pierce, the LA Times editor:
"Hey bloggers, there has been a little buzz surrounding John Edwards and his alleged affair. Because the only source has been the National Enquirer we have decided not to cover the rumors or salacious speculations. So I am asking you all not to blog about this topic until further notified. Keep rockin'" Tony Pierce (from Coulter's "Never Trust a Liberal Over Three")
It's a mistake to think of any liberal media source as anything but an extension of the Obama (or any Democrat) administration.
When the Juanita Broaddrick (alleged Clinton rape victim) story broke, Time magazine sat on the story. The story was broke by Drudge.