In my opinion, the stupidest thing Imus did was apologize. He should have just stood his ground, said it was a joke and everyone could get over it. Would his sponsors really have left? Maybe, but doubtful. They would have come back, anyway. Stern certainly went through it in his career. He'd lose some sponsors, but he always got more. This kind of stuff only serves to increase ratings and ultimately increase revenue.
If you think about it, in firing Imus they will lose the ad revenue anyway. But I do still think it's about money more than anything else. I heard a "radio guy" saying that it wasn't about losing sponsors as much as Imus being overpaid. He said Imus had low ratings and a high price contract. They wanted to get rid of him, and this incident just handed them a perfect reason.
Really, this is a winning situation for everyone involved (except Imus). CBS gets to appear morally outraged while relieving themselves of a financial burden. And Jesse Jackson and Al Sharpton get to further their agendas. And everyone in America who thinks free speech should be censored on public airwaves gets a win in their column. Way to go!
Just a couple of points:
1) His sponsers already HAD left. They notified CBS after CBS handed down the suspension, but before the decision to fire Imus.
2) Stern was an entirely different animal. He attracted more sponsers because his ratings were always high. Imus has LOW ratings, but commands the premium on ad time because his demo is "affluent". There is only a certain number of advertisers who want to "cater" to that group, so "wooing" new sponsers isn't as easy as it was with Stern.
3) They're NOT losing the ad revenue, actually. Or rather, they're not losing the profit on the ad revenue. Because there is something filling his time slot now that is less objectionable to the sponsers. There will be something more permanent filling his time slot at some point, and I'd assume that, too, will be less objectionable to the sponsers. And likely, as you point out, they will not be paying as much in "costs" for that programming. So they can take less revenue, but make MORE money, than they could if Imus stayed and they lost the premium paying sponsers.
4) Again, this has nothing to do with free speech. This is not an FCC ruling (and, likely, there won't be one. It's a companies decision. So it's not about censorship, per se. If Imus owned CBS, he'd likely still be broadcasting with no repurcussions, other than possible ratings and financial ones. If the FCC had levied some sort of fine against Imus, I'd be right there with those publically decrying the fact that the govt was abridging his free speech. But I think many people are much less likely to say that a company MUST employ someone they, for a justifiable reason, have decided they don't want to employ.