Patents are territorial. That is, unless someone has filed an application (or designated Australia as part of a national phase of a Patent Cooperation Treaty (PCT) patent application, nothing will issue in Australia. Generally, companies try to figure out where their likely markets are, and where the expense can be justified. Australia is becoming more and more relevant, but it was not nearly as common to file there a few years ago. (Full disclosure, I'm a U.S. patent attorney (but I'm actually a good guy!).)