These gentlemen are simply playing to their base, just as Sarah Palin does. There are very real finacial gains in doing this, which is one big component of their "belief" system , and they will always have uncondition support of this base under any circumstances.
Limbaugh and Roberston also know that the more that they are attacked for their particular beliefs (regardless of how nutty they may be to you or I), the more they will be supported by their base. It is an ongoing, simbiatically cozy relationship.