Fact is, for every member who signs up here, there are thousands who don't. They're content with just reading the content. Some of them will even say, "Why should I sign up here when I already have Facebook?" Some folks have both. Some hate forums and others hate Facebook.
To put another way, when contacting a company's customer service department, some people use email, others would rather call, while still others like to take care of issues face-to-face. Everyone is different, hence the reason why companies offer multiple methods for contacting them.
Facebook is no different. It's just another way for our visitors to keep in touch and interact with BassResource. So it's not an either/or thing, nor do you need to have both.
Hope that helps!
Glenn