I have had my Aura fall on on the floor and on my face while reading in bed; I am more careful now, but I have been lucky.
I worked with glass for many years in the lighting industry. For glass to fail, there always has to be a flaw
and a stress. Flawless glass (etched to remove any scratches) can be used to hammer a nail, as long as you don't introduce scratches with hammering. Likewise, glass with scratches will not break if it is not stressed.
Many of us have seen this in auto windshields - you get a small nick in the glass, and it will not propagate into a crack until you have a cold day and turn on the heat. The thermal stress will then cause the glass to crack.
"Prince Rupert's Drop" is an example of highly stressed glass - you melt and drop a "teardrop" of glass into water. It is highly stressed - When you snip the end it explodes! There is a cool demonstration of this in this video -
https://www.youtube.com/watch?v=13B5K_lAabw - and an explanation of glass improvements for cell phones.
My guess is that Gorilla Glass is not being used in e-readers. The very minor flaws that remain in the glass substrate, combined with the stress of a drop or a thermal shock are what make these wonderful little devices prone to cracking