It's sometimes difficult to differentiate between stress fractures and fractures that result from normal wear and tear. Granted that stress fractures or wear fractures that occur in the first week might seem abnormal, it would not be abnormal, in my opinion, for fractures to occur after that time.
In my own experience using these types of devices there are any number of things which might damage the casing. Setting the device down too quickly or in a forceful way on tables, counters, etc., oils from the hand, prolonged exposure to sunlight, excessive vibrations...
The point is that this device has been manufactured in a standard way, but the types and degree of usage by each individual purchaser is infinite. Even the most well thought out stress tests are no substitute for thousands if not millions of users and their varied experiences.
As with any mass produced product there will always be those who experience satisfactory usage and those who experience subprime usage. This is just a fact of life
