I work as an engineer for the company that manufactures the majority of the mail sorters used by USPS and all I can say is that Gamefly must be using some pretty crappy packaging for their disks to be damaged by the equipment.
Also, it's all the same equipment that the Netflix, Blockbuster and everyone else's packages go through, do Gamefly seriously believe that USPS has various grades of large and very expensive mail sorters sitting around so that they can allocate varying levels of service quality?