PR of those forums is much important. I guess with more sharing and linking these forums might have PR above 1. I found few more forums using big-boards directories. But those forums are highly moderated and don't allow sig links which are spammy.
That would explain why some of my casual replies get freakish reactions from admins who start screaming about "spamming". if I show upon a forum and write three replies for the year. how can that be spamming?
I thought spam was like 85 replied in one hour.