But they shouldn't do this either. Personally, I try to downvote--or at least not upvote--comments which I agree with but which add nothing to the discussion. (I'm sure I'm far from consistent, of course.)
I mean, the functional use of votes is to organize the comments page. It just makes zero sense to organize the page based on the average opinion of the community rather than constructiveness/usefulness of the comments.
PG is wrong here.