[pitaa]

I would bet there's more to it than just wanting "recognizable" trucks for residential deliveries. Using a box truck is less efficient because they don't typically have access to the box from the cab, so the driver has to get out and run around to open the door at each stop. But this isn't quite as big of an issue when they're doing commercial pickups/deliveries, because there's usually numerous packages at each stop, so getting out open the back isn't as much of a time sink per-package.