Every person playing within a particular region, example: Americas, will theoretically have access to all items within that region. However, with players using different currencies, they are limited to using only the auction house of their currency.
So for example the following could happen: An Australian player finds a very valuable and very rare item and decides to sell it in the auction house, but they can only use the AUD auction house, likewise any potential buyers must also have AUD accounts. Only players with AUD accounts can have access to this item even though the item was "in theory" available to everyone within the Americas region, until the point that it was found in loot.
I would like to know what Blizzard plans to do about this problem.