Reason they would release a new disc is to update the programming methods/graphics with the then state of the art methods. It would also allow them to roll over to new (and hopefully improved) servers that can support quicker/better processing. Technology advances so quickly, that it would be more beneficial to provide a whole new disc. Plus, people seem to respond better to physical merchandise rather than digital downloads because of the sense that they physically own the game, rather than a digital download that could be lost with a major glitch in the system. Just my take on it.