You're making it sound more complicated than it is. The idea is simple: users like to make objections.
Since users like to make objections, the initial comments tend to object to the article/title (because there's nothing else to object to yet), and later comments object to existing comments. Poof, "waves".
Since users like to make objections, the initial comments tend to object to the article/title (because there's nothing else to object to yet), and later comments object to existing comments. Poof, "waves".