Most of them use ad agencies that “bundle” advertising deals for them. They would usually take the extreme step of turning down business only if the company in question is indicted or otherwise known to be a PR disaster.
In this case, I am positive (not certain) that it would be difficult to have these networks remove Quixtar. After all, OUR Elected government considers them a legit company. It pisses me off too, but some of these fights are harder than others …..