The problem with your theory is that they only give “favorable” press coverage to candidates that are unknown. Pawlenty, Santorum, and the Indiana boys will probably get lots of great press until they compete.
In other words, almost every candidate will get somewhat positive coverage until they are the inevitable.
It would not surprise me if the MSM tries to prop up a well-known candidate like Romney during the primaries knowing that many conservatives and Christians will never vote for him if he gets the Republican nomination.