[citation][nom]Hanin33[/nom]jellico: Australians exist outside of the physical continent of Australia... their websites need to be accessible to more than just Australians either way... and what about the Australians that wish to access sites on net ranges that are filtered because zombies reside on them?[/citation]
This is simple pragmatism: you take defensive measures which will inconvenience a small number of people, but preserve services for the majority. Or you do nothing, because the servers need to be there for the people outside of Australia... then the DDoS hits. It overwhelms the servers, and now nobody has access.
A DDoS is a primitive, yet insidious attack. It is precisely because people unwittingly participate, via their zombie computers, that it is effective. Consider this: if you have a terrorist who is threatening to blow up something because he is a true believe, or one who is threatening to blow something up because his family is being held hostage and he has no choice, it makes no difference to the defenders. You shoot the guy in the head because it is what you have to do. It's as simple as that.