Gorilla Glass won't, and is not meant, to protect you from scratches caused my high-grit dirt (especially sand). Sometimes even the lint from your pockets or bag, if rubbed into the screen the right way, can nick it up. It's just physics...something with a higher grit level will always scratch up something with a lower one.
What GG is meant to protect you from are common objects you would have in your pockets. Pens, pencils, keys. Those sort of things. Lots of people think they are immune and then curse the phone when they see scratches. Even one grain of sand is enough to do visible damage. Screen protectors are the best for protection. I have had my LTE Gnex since last December, and with a TPU case and a high quality clear protector, my device still looks like it came out of the box on the first day.