Do you base that on your own experience with the iPhone? Are there studies that have been done that show that the iPhone 4 is more prone to the front screen glass breaking than phones of a different design (which pretty much does mean every other phone in existence since no other phone has the design characteristics you are describing other than chinese knock off iPhones.) Or are you just basing that on your personal Engineering judgement and expertise?
Physical dropping aside and screen shattering issues (which I maintain my position that it is just a reality of any phone that uses a glass screen); I would argue that the iPhone 4 design will take normal wear and tare better than a plastic smartphone design. I base that on the fact that all my previous phones looked terrible after two years of usage whereas my iPhone 4 still looks like a new phone (besides the small scratches and the dimple on the screen from dropping it which you can only see if you hold it up to the light). I also base that on my engineering judgement because of the selection of materials (glass/aluminum/steel) is much better for normal wear and tare than plastic.