This question started with some paranoid thoughts, but evolved into a more sane question.
I just noticed one of my comments on SO that I'd swear has been edited to be just slightly but significantly different, except of course that it hasn't. Obviously this is what I get for writing comments when I'm tired and distracted.
But it did make me curious - is there anyone who can (and would) edit comments? Apart from the author, in the first few minutes after making that comment, of course. And can anyone other than me delete my comments?
I'm guessing that the answer is no - that that is one huge mass of data that no-one would even think of trying to moderate in general - but might there be some exceptions?
For example, if there was a legal complaint about racist or otherwise offensive remarks in comments, what would the procedure be? In a question or answer, I doubt anything like that would last very long before "the community" intervened (though editing history might still be a legal issue) - but a comment is a bit different.