Earlier quoted context omitted.
It only takes about ten redundant comments (wild guess number) to derail a thread for thousands of would-be participants. This doesn't indicate community value; at best it indicates accidental nerd sniping, and at worst could be a coordinated attack on what would otherwise be a productive discussion, from which more people could derive far greater value.
But the comments are drawn from the distribution of Hacker News readers. You can't presume that just because you see a thread of ten comments as an off-topic distraction that so must the other thousands of readers, especially if there are healthy replies and up votes. Your comment that it "derail[s] a thread" makes the implicit assumption that the comments are actually off-topic. If they are on-topic, but you happen…
There was another example of derailment recently, with a dozen comments arguing over what a "middleman" is when the original comment was really about how best to support indie makers.
Anyway, thanks for the interesting discussion, and I hope I haven't made this thread less useful for someone else in the process.