That doesn't say they can't be forced to remove it if proved defamatory. It only says "allegedly defamatory" feedback.

I think if you won a libel action, you could force them to take it down, after proving it was defamation.

You shouldn't be able to sue eBay for the comments, since they didn't make them, but you can sue the speaker - the person leaving feedback.

The press always reports legal cases wrong and of course never includes a case citation!