Gorilla glass is not that strong. I'm not surprised it cracked when falling face down.
My friend has a Motorola Defy like me (you know, that "lifeproof" phone with gorilla glass), and she dropped it about a metre onto concrete, at a 45 degree angle. Whole glass panel was completely shattered.
On the flip side, I have dropped my Defy a bunch of times (including a few times where I have accidentally launched it forward a few metres) and it has been fine, but the initial impact has always been on the back. I think all phones will shatter when they hit the ground screen first.
Gorilla glass prevents abrasion and scratches from keys or coins etc in your pocket, but not falling a metre or two onto concrete or tiles.