Speaking about your other attributes... I think the most telling thing about the Pearl River Delta is that 2 of those 11 cities were governed by the UK until 1997 - and you still have to pass through customs and immigration to cross into and out of them...
The customs thing is interesting. Citation?
Also, those two cities I was talking about are Hong Kong and Macau. Both were governed by the UK from the end of the First Opium War (1842) until 1997, when control was handed back to China. The terms of the handover included maintaining independent boarders (and forbidding complete freedom of movement and immigration). You can read about it and the other terms of the handover here (http://en.wikipedia.org/wiki/Transfer_of_sovereignty_over_Ho...).
It's substantially easier to visit Hong Kong than China (visa at the airport vs. visa in your home country before you travel), unless you have an APEC card of course