A Body WAGONS-Ho! A body Wagon Thread

I don't have a Wagon but I have a Wagon related question that I have always wondered... Why did the 63-66 wagons get the more open, round rear wheel arches but everything else here in North America (4dr, 2dr, convertible and even the Barracuda) did not?
Great question. I am a Valiant fan, and Always liked how the wagons had them. Wish the car did.