Sorry, I made assumptions that people knew what gzip was. EDIT: That wasn't meant to be condescending, I apologise.
To clarify the original comment: I think it's rather pointless to gzip a PNG file, since PNG files use deflate compression, the same method gzip uses, and hence it has very little real benefit, if any.
Your look of disapproval seems to have overlooked why he said he was using it. He's clearly aware of your point, and even mentioned the uselessness: "Up to 1% savings" while explaining why: Google Page Speed is stupid.
Why do people always say "this is not reddit"? I never even heard of reddit till I saw those comments. And I think this observation made over and over again usually adds less to the discussion than the politically incorrect statements this comment is made in response to.
Also, I don't think your link relates the the comment. Your link is about choosing between gzip and deflate; the comment you found objectionable was about the irony of gzipping a file that is in a format that also support deflate (so you might compress a compressed file; which I think can actually make the file larger).
Many on HN were once / still are redditors. Especially proggit. The type of response where you quote part of the parent, don't add any comment or commentary, isn't especially helpful.
Addressing your second point: I also thought the comment was a snarky reply, wondering why someone would use gzip instead of deflate. The parent comment addressed, specifically, why they were using gzip on PNG, which is why I assumed the 3 character response was focused on the compression type, rather than whether to use it on PNGs.
(http://stackoverflow.com/questions/388595/why-use-deflate-in...)