How would this be any different from the Nokias and Sony Ericssons? A drop is a drop, and whenever that happens, it depends on how high it drops from, and if it is protected. I reckon that cases would absorb and distribute the shockwave around the case more than silicone cases, therefore providing more protective properties. But it makes no different if it is dropped from several storeys up or if the case protecting it shatters to pieces and pieces the body of the iPhone.

A drop is a drop. The only worry I would care about is avoiding it, or the kind of protection it has when that unfortunate incident happens. If you cant avoid being a clumsy klutz, then the general rule is not to buy expensive phones, but rather buy those that can take a few beatings of its own.