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.
No, they should be required by law to provide goods without deception, otherwise I've got a lovely bridge you really must buy. That is what the consumer protection of sales is about, providing confidence that you're not being scammed by offering legal protection for the transaction/quality of the goods. It makes everything better.