Australia does allow dual citizenships. Usually crown countries are granted the ability to have dual citizenship with the United States or vice versa. Though it is a lengthy process and it really depends whether or not the origin of the parents. Even though I'm a natural born United States citizen, who relocated to Canada. What granted me the ability to get dual status as a Canadian was my parents, which where both natural born Canadians. Hence by default, I had the ability to get into the pool to be able to gain a dual citizenship.
Though it took me almost 15 of the 20 years I've lived in Canada to actually be granted my status. The road to citizenship is a long tedious process and there are lots of restrictions and as well cost associated. Why most people don't tend to go down that path because it is really a crap shoot, but is more than worth it when you can get that form of status, especially dual status. Countries like Canada have very strict criteria to be able to gain citizenship beyond what most people tend to think, Canada has some of the strictest immigration policies in the world, but it is possible