I'm not really the big guys here on StangNet (that's my quote above - I'm an admin elsewhere), but those are the most likely reasons behind eliminating the regional forums, since the national classifieds have been moved onto the forum itself. The change in classified systems itself is because the old system never really took off. Corral, for example has an extremely busy classified section that's based in vBulletin. Ours was a third party system that was foreign to most users, and I can only speak for myself, but I know that I've been a member at other forums that weren't based on vBulletin and I have a tendency to not stick around at them very long. Maybe I'm just lazy and unwilling to learn a new forum software, but I prefer to stick to what I know, and I'd venture to guess that our old system was looked at by others, in the same manner.
The new system can be made just as effective as the regional system if we institute some ground rules for the classified sections that include a location requirement. I've been looking around for a plugin that allows you to search by location (or similar function), after hungrymonkey mentioned it in the thread we have going on this in our staff forum. In the meanwhile, simply adding your location to the thread title at least makes weeding through them a bit easier. We're always in favor of improving the forum for the members and moving the classifieds onto here
should make it better in the long run. Just give it time, we'll perfect it and it'll be like it's always been there.