Imus' audience didn't even know it was politically incorrect until Al Sharpton and Jesse Jackson told them so.
It wasn't audience reaction that caused CBS to fire Imus. It was the race-baiting lobby.
It was the fact that his advertisers bailed out. To some degree, that was brought on by the fact that advertisers did not want to be associated with him on a national basis. But a lot of it was that his own listeners pulled the plug, and his advertisers followed suit. That last part is not going to happen with Rush.