It is these types of postings which go against the beliefs of the newsgroup that I think would elicit flaming. People start new threads all the time. Well, my feeling is because either they don't want to talk about a certain topic anymore, or they just simply have a new topic to discuss. Rather than keep posting follow-ups on the same thread, especially if there is something else which the person wants to say, a new thread can be started. If they do have something relevant to say on the topic, however, then a follow-up would be more appropriate.
Threads keep going because of interest in that particular topic.
It all depends on how much interest the thread provokes. Responses to messages can also be extremely predictable. Since most of the messages in both my newsgroups are mostly questions, the prediction of a response to the question would be fairly feasible. In this sense, responses to messages in my particular newsgroups are extremely predictable. If one were to predict what types of response were to follow, then it would seem pretty obvious that information regarding the question would follow.