To be fair, I don't think XiXiDu expected special treatment for being a donor; he didn't even mention it until Eliezer basically claimed that he was being insincere about his interest. (EDIT: Thanks to Wei Dai, I see he did mention it. No comment on motivations, then.)

I think that Eliezer's statement is not an expression of a desire to give donors special treatment in general; it's a reflection of the fact that, knowing Xi is a donor and proven supporter of SIAI, he then ought to give Xi's criticism of SIAI more credit for being sincere and worth addressing somehow. If Xi were talking about anything else, it wouldn't be relevant.