My take, which is by no means any more valid than anyone else's, is this: There aren't enough inherent differences between "pre-ban" and "post-ban" firearms to warrant a separate forum. You can certainly start a thread or two on the cosmetic differences between the two, but I can't picture an entire forum dedicated to "pre-ban."
BTW, I think that starting a thread on "pre" versus "post" would make for very interesting reading in one of the forums. I hope you start one!
-Dave