Ereader screens are not hard to break. My husband had his in his briefcase in a cover, and he had also put a wine bottle in the briefcase to bring home on the train. The pressure of the bottle against the screen cracked it quite nicely.
It was a Kindle 1, and happened perhaps two years ago. I took it apart to see how it was made, and it appears to me that almost any pinpoint pressure will be enough to cause a crack.