I think that initially posting at forums can be quite frantic from new people and this may last a month or so but that can soon tail off. As for WAB, as has been said, perhaps people join up just to get something ID-ed then they disappear.
I've known very few forums where I would actually
want to continue posting after say, thirty posts for example as for the most part they tend to have an inner clique that won't let anyone else in and you end up posting with no one replying. WAB isn't like that, actually this is one of the nicest places I have found and I've felt welcomed from the off
