This is what I came here to say.
I worked on the K&L ads personally, and I had a front-row seat to the whole debacle.
The ads were originally supposed to point to the GS review page, as they sometimes do. When the review came out, Eidos was understandably upset, and yes -- they did threaten to pull the whole campaign -- but they eventually simmered down and kept the campaign. They had us change the clickthrough URL from the GS review to the official site, but other than that little changed.
The ads went up and the Eidos brouhaha was settled over two weeks ago. Jeff got fired yesterday. Furthermore, I'd heard a few people tell that he'd already been skating on thin ice for "unprofessional reviews and review practices." I don't know much about that, though, so I can't say one way or the other.
My gut tells me that he got canned for larger reasons. Maybe the Eidos debacle was part of it -- I don't know. But I sincerely doubt that Eidos made Gamespot fire him. CNET doesn't kowtow to its advertisers, and I've more than once seen the higher-ups turn away big advertising dollars for the sake of the company's integrity.
I think the whole thing is likely a combination of factors, the biggest being poor timing. Gerst gets canned just two weeks after the K&L incident, so people blame it on that (especially when backed by PA, the gaming journalism equivalent to The Daily Show).
It'll be interesting to see how everything pans out, but I'm definitely gonna keep an open mind about it for now.