Good point. Try on a longboard on pavement. You'll figure out pretty quickly why a positive angle on both feet is better for carving. I find that is also much less straining on your back knee.
I've never done skateboarding and I don't think I ever will.
I do find that a duck stance is significantly more comfortable for me, allows me a much better movement range, is much more comfortable for my knees and less tiring for my leg muscles.
I'll happily sacrifice a bit of carving performance for a duck stance.