It is actually a good question.
I think we can all agree that we should invest some money and care protecting our device. I do not understand people that wants cheap things on such an expensive phone but they exist, so it is ok.
I like to use a good case like the leather one from apple and a back protector. It works great and with some luck (!) the iphone stays perfect.
Yesterday I checked an iphone 4 used by one of my parents. It is protected by a plastic case (not a cheap one but still plastic) and the film protector on the back is in horrible conditions, like really horrible. What does it mean? In my opinion, inner material is a factor when you are choosing a good case and with some care (and luck) your device will be crystal clear.