I believe that is what he's trying to say. You don't use Arial because it terminates at right angles, you use it because it feels different.
It's like art: you develop more sophisticated tastes as you're exposed to better things. It's hard to say this without sounding snobbish, but if all you've seen is Arial, you'll find Arial familiar and comfortable. But the more time you spend looking at good typography, the more Arial will start to hurt your eyes.