On the Internet no one cares about punctuation or grammar.
Maybe you're overthinking it. People just don't like to hear about something that's completely irrelevant to the conversation.
If you really care about improving some one grammar, send a private message. It can be very useful for a non-native speaker, especially if it's not a total stranger to you. Saying out loud "fix your grammar" doesn't make you a hero on a white house.
Not surprising, even looking at some of the appalling written English posted here on HN (a community which, you would think, is educated to an above-average level). Nobody cares. Plus, if you actually point out incorrect spelling, grammar, or usage here, you’re instantly shouted down with cries of “language evolves!”
[Edit: Looks like the “Language Evolves” crowd is already here!]