Specifically, this is a threaded comment system. We can have as many discussions about something (post or other comment) as we want: go off on wild tangents, point out the spelling, have a pun thread, mention patterns of blogging/commenting the parent fits into, reply to the author on a separate subject, share anecdotes related to the subject of the post, and actually talk about the content of a post or comment, all at the same time, without breaking anything. That's what's so neat about threaded discussion: it doesn't require the "comparative notability" that a linear conversation needs in order to function.