A "nerd" and Engineering comment...
eink and LCD screens, are prone to breaks by tension and/or compression (they are mainly crystal displays or a layer of it). If the device itself is not bend or receives a big impact like an accidental drop without a cover, it should last for ever.
For scratches, any cover should protect.
I personally never put any ereader, laptop, netbook, etc, inside a luggage or package that I don't carry on myself, in order to avoid damages by a shock or accidental tension (heavy stuff on top of the backpack)