Regarding point x, it's not that screen size is calculated on the diagonal; doubling the diagonal (and keeping the same aspect ratio) doubles the width and height as well.

The key is that area is the square of any linear dimension (again, for fixed aspect ratio). If you double the diagonal, you quadruple the area. If you increase the diagonal from 7" to 9.7", you almost double the area (1.92x to be precise).