We don't have a free market. There's a price to pay for advertising on Rush and Beck. If we had a free market, companies would not give in to terrorists like signon.org, Color of Change, and Media Matters.
You're giving these organizations far too much credit. Rush would be the first to argue that there are plenty of advertisers for his show, who aren't intimidated, in the least, by a relatively small number of names on a petition.
The fact that these other companies step forward and plunk their money down and advertise on Rush shows that nobody really needs to be intimidated, if they don't want to.
What really happened to Rush is that he proved himself to be dangerous to their good corporate and product names. They don't want to be put in a position where somebody, they can't control, can damage the public perception of their corporate images. Rush made a mistake, and insisted on making it worse for a couple of days, and then apologized, which indicated that he was wrong from the get-go. These big advertisers want to be associated with responsible broadcasters who exhibit good character, add to their corporate image, and help bring in business. The last thing they need is to be associated with a loose cannon who could blow up in their face causing them expensive PR problems, and future revenue.
It is a "free market" and the fact that advertisers are free to place their ads where they want proves that it is. You might say some are "corporate cowards" who have retreated in fear, but others would say they are just "smart business people" who are highly focused on their own bottom line, and don't want to get involved in petty, imaginary, and often delusional political battles where they don't want to be seen as taking sides. There are many other places to advertise that don't have those same silly dangers to their corporate image, and bottom line, so why take the risk when they really don't have to?