It's available worldwide on Amazon Prime. So yes, it is available in Australia, but you have to pay for it. If you choose not to, that's up to you.
For me, it's not a question of choosing not to. I simply want my own copy, one that I can watch again and again, without having to rely on the whims of others -- be it Amazon or other types of TV.
I just want to be able to watch this particular show whenever
I want to. What's so hard for Amazon to understand about that? *crosses arms, taps foot, a la Tiffany Aching*
Besides, I don't see why I should pay Amazon anything. Since I live by myself, work during the day, and use my computer in the evening, neither I nor anyone else will be there to watch anything on Amazon. I may as well just throw my money in the Ankh. =P