You mention it but I just want to reinforce it. I don't go to PH at all but I see the issue on HN all the time. People writing a comment and suddenly the "at [company], we bla bla..."
It generally annoys me when I see it no matter what site I'm on but you're right, on here it's rare and more importantly this is HN so you should expect a bit here and there. Most of the time these people are just excited about something they're creating.
If people overdo it, we ask them to stop (and in extreme cases ban them), so feel free to email hn@ycombinator.com if someone is overdoing it.