Bear with me now, but I think the iPhone's protruding camera could be a hidden benefit. With the larger size of the iPhones and curved edges and screen it is naturally going to be a bit harder to handle and not drop. This is one of the reasons why the vast majority of people use cases on their phone. Now let's say you designed the iPhone knowing almost everyone will put a case on it. You could make for a thicker phone and have the camera be flush with the encasing. Or if you have the camera protrude a bit you can make the entire phone thinner and the protruding camera is meaningless since the phone will always be in a case. So basically if we did have a flush camera then the iPhone would be much thicker when you add a case.