In the days before power steering was common, the steering wheel had to be quite large diameter. I suppose a good way to try and provide a bit more leg clearance on the Austin. Seem to remember driving a Rover SD1 with a squarish steering wheel.
I guess the wheel you are looking at is trying to look like a F1 car wheel. Seems Mclaren gone a bit square. Might work as something you don't think about is how far we turn the zed wheel to turn. Thinking about my zed wheel, seems to be about 90 for 90 turn (correction 360 for a 90), which is quite good. My wheel as it stands obscures the top of the dials in it's most comfortable position.