The glass is reasonably scratch resistant and also very flexible (as shown in Apple's iPhone 4 video). The problem is that the flexibility is absolutely useless for this particular design, since there is zero flexing allowance for energy absorption once the glass has been glued to a hard surface. On impact the glass is caught between a rock (the ground) and a hard place (the phone), so to speak.
Bingo! so the bumper needs to be raised (more) above the glass front to absorb the energy. Not sure if it's possible based on the design, but a more flexible adhesive might be worth looking into.
One of the things I do is create realistic detailed models for a forensic animations engineering firm, used in accident recreations, which involves a lot of "impact".