It isn't the amazon.com site that concerns me, but the European sites: principally amazon.co.uk, but also amazon.de and amazon.fr. There are many classical music releases in Europe available on the .com site at double the price (and of course not available at all on the .au site) of the .ukl site when they can be had at all; it's not surprising, since the classical record labels are run from Europe and that's where the music originated. Likewise, there are cinema and TV releases of varying obscurity, and Australia is in Blu-Ray region B.
Delivery from the UK has usually also been much faster than from the US, typically a week. Although the last one took a month—perhaps they were softening us up?
All statements so far have been that we'll be able to order most items from the .com site via the .au site. Not a word yet about items from the .co.uk site. And no sign of the email from them either.
Given that only fresh food is exempt from GST, and it can't be imported by mail, how hard can it be to charge 10% GST on anything shipped to Australia? I think this has more to do with trying to make their Australian warehouse viable.