I've seen various reports about the regional block. I'm not 100% sure what the boundaries are, or if it exists at all---it could also be a convenient excuse used by an RCI VC to get a persistent person with insufficient trade power off the phone. If anyone has an otherwise-tiger located in Central FL that can't get DVC, I've yet to hear about it. On the other hand, a friend of mine who owns at HGVC-Intl. Drive was able to exchagne in, Weeks-side, but as that's a mini-system, it may have its own rules.
It's also not the case that Points resorts cannot have 1-in-N rules. Points inventory is not subject to 1-in-N rules, but Points resorts can have inventory in both Points and Weeks. In the OP's example, Orange Lake's four resorts are Points resorts, but their weeks-side inventory is subject to a 1-in-3 rule across all Orange Lake properties as a group.
It is generally at the behest of the resort with the rule---some resorts view this as a sales tool, "You can't stay here unless you own here." RCI is the point of enforcement, when the exchange is confirmed. Every once in a while they let one slip through, but it is rare.