I can say from a perspective inside the radio advertising business that it has become very specialized in a bad way, to the point where potential radio advertisers are increasingly becoming companies that seek one-time impulse buyers, or are offering products or services that will rope people into a monthly credit card charge.
The industry has become almost exclusively what they call "direct response" advertising. You hear the ad, and you're asked on the spot to call an 800 number or visit a .com. The success of the campaign is based entirely upon the response to those 800#s or urls. Repetition is still in play, but the nature of the response they seek is immediate, rather than part of a long-term marketing strategy. This severely limits the kinds of companies who advertise on the radio, to the point where it's almost exclusively companies that offer things most people don't want, but who view the success of a campaign on a "sales per day per market based on response" criteria.
The "legitimate" companies - Sleep Number, Rosetta Stone, Oreck, etc - advertise on a prominent national show like Limbaugh's. The others - male enhancement, miracle skin cream, collector coins, etc - are the clients procured by the local affiliates.
My point here is that the "legitimate" companies looking to advertise nationally on a show like Limbaugh's are finite. Direct response radio doesn't work for every product, or every business model.
From my perspective, now that I've seen the advertiser fallout, it is clear why Limbaugh apologized. A commercial radio program only remains viable so long as advertisers are willing to spend. Limbaugh has so far commanded the highest-buck players among direct response advertising clients. If he loses them all, he'll have to replace them, and that will not be as easy as we think. The Rush Limbaugh Show as we know it will not survive pitching prostate tablets and glorified car wash tokens sold as "mint collector coins".
