I was actually thinking about this (sort of) on my run yesterday. Well more specifically I was thinking that there are 2 distinct different ways people approach this.
They come, spend a lot of time on the forum prior to their IM and then disappear, or they become serial IM participants and forumers.
(I do realise that disappearing from the forum doesn't necessarily mean they retire from tri, but I think a lot of them do).
Not a criticism btw, just an observation.