It was OK for the MSM to cover Ron Paul's campaign as long as there was no voting taking place. After all, they have to have SOMETHING to talk and write about, and all the other candidates sing the same old boring tune. But once the voting started there has indeed been a complete MSM blackout.
Economists William Meckling and Michael Jenson, formerly of the University of Rochester, offered an explanation for the extreme statist bias of the media some thirty years ago, and I think it applies to the MSM's current blackout policy. If you are a national news reporter, you must always keep in mind that news must be new. You must cultivate numerous "inside sources" of news, and in today's world those sources are overwhelmingly in govenment. If you report on defense issues, your main sources are Defense Department bureaucrats or political appointees. If you are an environmental reporter, your sources are EPA bureaucrats and political appointees. If you are a crime reporter, you rely on the FBI bureaucracy, etc., etc.
This is why the media are never very critical of government bureaucrats -- unless the bureaucrats are being insufficiently interventionist. They pretend to be critical from time to time, but not really. The regime must be defended at all costs, for it is the regime that is the source of the journalists' human capital. Strip away parts of the regime, as Ron Paul wants to do, and you strip away jobs and careers for "journalists."
It's not Ron Paul who is the target of the blackout, but his ideas of peace, freedom, free enterprise, and limited constitutional government. After all, the MSM never, ever write anything about him without saying, "but of course, he has no chance of winning." They don't believe he could ever win, but his ideas could, which is why they must be hidden from public view at all costs.
It will be interesting to see how much longer it takes the internet to break up this monopolistic political conspiracy.