I am not really sure, i think most people see this items as indestructibles and they treat them as any extension cord, they trow it to the floor and breaks or something.
In my experience I have 4 chargers and have never had trouble with them 2 of the square connector version 1 of the newer ergonomic version and 1 of the newest magsafe2, you had to take good care of them try not to flex the connectors and not to drop the box if that is the case you should have no problem.