Thanks for your comment. I don't know how ordinary US Americans refer to Australia and whether they use 'Oz' to do so but I am not surprised to hear from you that they generally don't. What I was talking about, and where I should have been more specific, is how Australia is referred to in the US media where I have quite often seen it called 'Oz' (and perhaps for the mundane reason of making for a shorter headline). This isn't nearly so common in the Australian media.

Btw, I agree with you that US Americans often mispronounce 'Aussie', but I can understand why, if they encountered the word in print before hearing it spoken.