There are some computational issues and the shapes are not as rounded as they should be. You can see that passed the 11-norm, it feels like the shapes are the same. That is partly computational issues with the system. Any way as p grows, the p-norm unit ball gets closer and closer to the filled square [math]-1\le x\le1[/math] and [math]-1\le y\le1[/math]. That square is the unit ball in [math]l\infty[/math]-norm.