I don't work with Fords, so I can't answer your question specifically. In general, the trend in cars is to have fewer controllers and devices on the bus controlling more and more things. In the VW/Audi world, all of the "body control" stuff is handled by a single module under the dash.
At the same time, many of those modules and the wires between them are accessible easily under the hood. I can reach under a VW, remove a plastic underbody panel and get to the powertrain (most important) canbus without opening the hood. I'd come up greasy, but I could certainly do it from under the car. With a little practice, I could probably do it in under a minute.
In the VW case though, that wouldn't do any good. I couldn't start the car or unlock the doors (door locks aren't on the powertrain can and the gateway won't pass through a door unlock message originating on powertrain). I could monitor their engine/transmission/ABS though and could turn off the car, change the gears or set/adjust the cruise control once the engine was running. I might even be able to trick the ABS into thinking the car is skidding and get it to lock up the brakes (I haven't played with ABS controllers much, so I'm not 100% certain of this one),