I think the problem is that it's difficult to listen to anyone, day-in and day-out, and not have them grow a bit stale. I love Rush, but I only listen to him a couple of times a month. Even he can become stale.
That and he never changes his rah rah Republican cheerleading and his fawning adulation of Republican big government. If he EVER said anything critical of Bush (like for example that he supports the semi-auto ban) I never heard it. Boortz at least fires off occasional criticisms of both parties. Listening to Hannity is like listening to a two hour Republican infomercial.