Let's also not forget that everything in live has an assigned and a perceived value. Now that radio is the corporate machine that it is, I think the endorsement structure is one of the last things that actually gives the low-on-the-totem pole talent a small measure of control. That is because the talent still, to a certain degree, has some control over their image. And, that image has real and perceived value.
This is a rudimentary analogy, but, let's look at the centerfield scoreboard at Turner Field. To the right of the mega-megatron, is a massive Wachovia ad. Is it there because the Braves love Wachovia? No, it's there because the Braves know that a crap-ton (scientific measurement just approved by the International Society of Weighing and Measuring) of people will see it over the course of a season and that Wachovia will pay a butt-load (see above) of money to have it there. Same thing. Two million eyeballs (not including the occasional TV shot) a year see the Wachovia thing. How man people a year put their ears on a product ad? It's no different, and it allows working on-air talent a way to monetize something that they own that has value. Just like if you are a wiz with tax returns, can paint a beautiful picture, can build a house, are good looking enough to get paid for people taking your picture, et. al.
Capitalism... Receiving value for something that has actual or perceived value. And, I guess I'm glad the jocks still have some latitude to make a little more money on something that they own. Their image.