The reasoning I suspect is more to do with price differentiation. It is easy to charge more to Australian consumers and I bet this is a business/commercial deci

The reasoning I suspect is more to do with price differentiation. It is easy to charge more to Australian consumers and I bet this is a business/commercial decision on Amazon's part more than it is to do with the technicalities of their back end. By blocking the other Amazon websites its easier to force Australians to pay more for their shopping on Amazon for the same products on their US Store (even with GST + Shipping).