That credit is wrapped in all sorts of terms and conditions - not US resident, but US customer.
In my experience - Amazon has a list of these US warehouses and its constantly updated. Products that I've previously purchased were at some point unshippable with the error 'We cannot ship this product to this address' or something similar.
When I used to do the US shipment route - my primary address was set to the US and had changed the address of my HK credit card to match the shipping address.
Your call .. they know its a warehouse and they know that you're using a non-US credit card.