I noticed this with Australia as well, I was just going to select one of the other countries since it appears to ony be a digital download anyway. Maybe I will email them and double check
Edit:
Decided stuff it, it clearly says digital distribution so I placed the order and selected a different country but added a comment in regards to been in Aus.
Got my confirmation email and it says I will be able to use the attached code to download the game through Steam once it's released.
Makes me wonder if it will be purchusable directly through steam? Will probably be cheaper if it is lol