Huckabee is on FOX, Limbaugh isn't unless Greta van Sustern plays clips of his show. That does give Huckabee a little more exposure in the conservative market. Limbaugh's TV show and his NFL TV job did not go over well, I don't think he is mainstream enough for TV.
Everything runs it's course I guess. CB radios, Bell bottom pants, TV Westerns, now talk radio and American Idol.
If corporations leverage up to expand, then face hard times because of it, I am sure that is something Limbaugh would defend as part of the wonderful process of risk taking and capitalism. Most of his sponsors seem pretty narrow, with about 60% being conservative groups.