Poor choice of materials?
Why would Apple design the phone out of such easy to damage materials in the first place? Mobiles have a tendency to be thrown in pockets with scratchy items such as keys, lighters, coins and are often thrown onto tables or taken to the beach. As a result, most touch screen phones now use gorilla glass to try and stop scratches on the screens, as well as thin screen protectors.
Seems like a poor design decision to me. If you have to wrap your phone up in a protective casing, all the effort into designing it thin and light is simply wasted. And as a fashion product, if it looks like shite within a couple of months because of the marks it picks up, once again all that design effort is wasted.