Yes, I think you are right.
I presume Amazon AU charges in local currency, although I don't know for sure as I haven't transferred either my book account or my Audible account over to Australia yet.
Firstly because I didn't know if the range was the same, and secondly because I wasn't confident that I could always just go back to the US account, and finally because I always swore I wouldn't do it until Amazon had a full Australian store.
The currency exchange fees bite, however
