If the occurence has been under-reported, I'm not so sure it's due to any media-wide desire to bury it. There's an old adage in media circles about there being no such thing as bad publicity. CNN is going to be reluctant to overexpose a story that gives free publicity to MSNBC, even if it's bad publicity. Remember, it wasn't that long ago when nobody on a televsision network would even say the name of a campetitor on air in any context, positive or negative. They were all just "another network".

As for the Imus thing, television doesn't really look at radio as direct competition. Giving free publicity to a radio station is no big deal. Most people only listen to radio when they can't watch TV, like while driving.