Gorilla glass is scratch resistant, not shatterproof. I have broken many a screen running nekkid. That said, I buy insurance and have since bought an otterbox defender. I work construction, and am constantly jumping off machines, and into excavations... tons of opportunity for me to wreck my phone.
They are very tough, but the shock of a short drop is enough, especially since they use nearly all the real estate on the front for screen. The glass is in very close proximity to the hard as nails kevlar that backs it, and provides little or no shock protection...