It's an anti-flamewar device to hide the "reply" on deep threads. You can just click "link" and reply from there, though.

I'm be interested in hearing what you have to say, so I'd be much obliged if you'd continue posting. ;-)

Sigh.

Do you nerd out on this stuff too?

Yes, and I also nerd out on the design of online discussion forums. So watching this discussion trip over a misfeature and nearly fall into the darknet was sad, and sad again.