1) These forums are about AMVs, but they don't represent the entirety of everyone who makes AMVs. Some people just don't get into the forum thing. I hear tell that there are people on the internet who don't talk at all, but only lurk. Spooooky.
2) These forums are about AMVs, but also about side chatter - moreso in the journals now, I guess? Even though there's no on-site OT, people still talk by the very nature of the thing. That way, people get well-known for their personalities as well as their editing. So the site, overall, is not only about AMVs.
So yes, that would be correct, forum presence does not directly equal anything except forum presence itself. In either direction. They aren't really related factors at all. (do I need to get out the "these factors are not related" chart again?
