Amazon open box deal on A77/16-50

True, the camera did not come with the Sony warranty - which is why I bought the one year warranty for $45.  Amazon does include a 30 return period.  This seemed like a better deal to me than getting a used one on ebay with only the remainder of the warranty period available (if the seller includes the receipt).  It is not clear to me why the original Sony warranty is not valid though.  It seems like the remainder of the warranty should be usable  - just like if you bought the camera from the original owner.  I guess it is some type of agreement that Amazon has with Sony.