The reason that we, Americans, can not hear the difference between an English accent and an Australian accent is because we are from the US! It is that simple... And just as recent post stated, you probably would't hear the difference between an accent from Northern California, Southern California and Oregon.
Also, it is really silly for anyone to get affended by differences in language because the way that I see it is... IT IS AMAZING AND BEAUTIFUL and just goes to show the evolution of languages, cultures and community as well as the complexity of humans and life in general... (GOD is awesome)