Given HN doesnt actually notify you of upvotes, I don't think "upvote as acknowledgment" works that much anyway.

Having said that, it's true that I have a lower threshold to upvoting an insightful comment when it's a direct reply vs the general thread.

And similarly, a rude comment is left intentionally ignored; I'll admit I get a bit of satisfaction in the thought that they'll never know if they were talking by themselves or I simply didn't dignify them with a response :p