It's not as simple as he's making it look but he's right about it probably being coded in way that should've been "easy" to switch offline. I'm imagining there is a region service interface on the client which is implemented on the server.
They could take that service and instead implement it on the client and I see no reason that most home machines couldn't handle simulating the traffic/commerce in a single region. The cities don't run when you aren't playing them so they essentially just become an assortment of stats that govern their interactions with the currently live city.
I'd say the reason they're doing it on EA's servers (other than DRM/DLC) is not so much for the region simulation (well they'd have to for public/MP regions) but for the "world" components like leaderboards and commodity prices.