The glass is probably stronger than the aluminum. With trying to make everything tight via screws and glue, the aluminum (because of the thinness) will bend and give way to the pressure first. The only thing keeping it in that shape is the surrounding outer band of aluminum, and it happens that the place where the lower volume button is at is a big hole, so that place will give in to the pressure first (it is near the middle). Aluminum is softer than the metal used in the 4S for the outer metal band. They should have used liquidmetal for support near the outer band in the weak spots (maybe near the button holes). I think this is a structural engineering issue during the design stages, or it could have been revealed during long term quality control or stress test (if they even have that at apple). I can almost guarantee that light pressure near the middle where the lower Volume button is at will bend all iPhone 5s (like sitting on it). This is bad news. I don't know how they can fix this. Can they use stronger aluminum? I think the only way to fix it is to use different material for the back, but it would have to be strong, the same material as the 4s. Liquidmetal will do but it is probably too expensive.
