I want to point out one more pattern that I also have observed:
Now and then, there's a flame war going on in a given thread and it happens that a side banter comes out of this. To provide an example someone may mention a recent game match in middle of a flame war and this starts a banter. This banter is good, and actually may be interesting to others (I was) but the fact is that the banter is in middle of flame war, of which I don't want to be part of. As the banter continues, the thread (with all of its baggage) get bumped up and thus reminding of the past flamewars which only begets even more flamewars.
The point here is that this kind of set the tone. If this isn't the tone we really want, then we may need to re-think about how we are moderating the threads and encouraging positive discussions or playful banter while dissuading continuation of a thread for where the horse is utterly, absolutely and beyond a shadow of doubt long ago dead. This, IMHO, would be more effective policy toward "flame management", I suppose.