I have no explanation for the difference. I have noticed the friendly, non-confrontational nature of this board as well. I have a couple other experiences that are similar.
I belong to a couple of scooter groups, neither is Yahoo based. One is inhabited, it seems, by people who are looking for the opportunity to show off their superior technical knowledge or to pick a fight. The other is of a somewhat higher level technically (as far as useful information to the user is concerned), and much friendlier to be a part of.
I've found the same sort of thing in guitar forums. In fact there is one group who got fed up with the bickering and nastiness on the original forum, so they broke away and started their own forum which is much more laid back.
As far as this group goes, if you look at the pictures of the bikes and their people it's hard to miss the age group we seem to represent. Lots of grey hair and beards in this group. I fit right in age and appearance wise.
I think there are a couple basic truths about internet communication that most on this board seem to know:
1. The harder I work to expose your ignorance, the stupider I look.
2. There's nothing dumber than an internet arguement.