A private company can't just do whatever it wants. They are immune to law? If abortion is illegal in a country I can't just open up a "private" clinic. If it's against the law it's against the law, and in this case Australia may have a law that would force Valve to offer refunds.
Okay, not really at all what I was saying there. A company can't break the law, sure. I can't open Josh's Murder Co. and go around killing people because it's a "private" business.
I'm just saying that when governments make specific laws that dictate the policies of a privately owned company, it can cross some sketchy lines. A business should be free to create their return policies as they see fit, just as consumers are free to not shop there if they don't like said policies.