Yeah, I don't see it as a "big deal" per se either. On the other hand I do spend a bit of time removing the fake sigs from posts that I quote and people seem to be getting a bit defensive over it.
I don't think it adds anything to the readability, if anything I get a bit puzzled when I'm dealing with those huge quote runs. There are already rules for what content sigs can contain and how it is displayed, putting it in the body of comment text seems a bit superfluous and an attempt to escape that. The absence of a rule against it seems a bit silly, there is no rule against me posting haiku in the bottom of every post but I don't do that either (yet!)