Let me try and make this clear. But I can only talk about the US.
In the US, the IRS assumes all income is taxable, unless you can prove otherwise. Because of the tax treaty, you have two options on your US tax return.
1. Declare the super income and pay US tax on it along with all your other income.
2. Declare the super income and then claim exemption because of the tax treaty. (You will still pay US tax on your other income, of course.) In other words, you have to show the income, then claim exemption. You can't ignore it. (Like math class in school, you have to show your work.)
But, if you rely on the treaty to make the income exempt in the US, then you must follow Australian law to pay any tax that might be owed under Australian law. Relying on the treaty means you are telling the IRS "this is not taxable in the US because I am following Australian law regarding this income." So you need to follow through and do that. The Australian tax might be more or less, I have no idea. But your choice is to pay all tax in the US, or claim the treaty to skip the US tax, but if you claim the treaty, you have to do whatever Australia says you must do.
