Design is both how it looks and how it works. If you take the Desktop WIMP UI, and try to come up with a way to redesign it work with only touch instead of mouse and keyboard, you'd roughly be already halfway to the iOS homescreen in terms of design. Instead of clicking on a icon, you touch it and the app opens, swipe to see multiple homescreens since desktop space is limited on a phone, add in a dock at the bottom. Contrast that with Metro. So that screenshot is NOT irrelevant.