Why is the Dell Australian Site more expensive than the Dell United States store?

Even after customising the Laptops to be exactly the same it is still a lot cheaper to buy from the American dell site. With the Australian Economy as it currently, why is it still so much more expensive?Why is the Dell Australian Site more expensive than the Dell United States store?I believe the US dollar as more value to it so its costs more with Australian money. If that's not true it could be from a reason such as shipping price differences.