From what I've gathered, there have been some substantial (but by no means wholesale) changes to HN behavior since then. There is a tension between how up and down work. I can't imagine we want a bunch of "me, too" comments to show agreement, so upvotes are a way to express that.

It would makes sense to consider downvotes similarly, however they also grey out the comment, so they aren't symmetrical actions. I've pointed out 'pg's comment myself in the past, but don't consider it a great practice now. As you note, it's useful for historical context.