Two minor corrections, assuming wikipedia is correct in it's paraphrasing of the impact of this law. Australia does have a slightly modified jus soli. If you are born in Australia and live there for the first 10 years of your life, you are granted citizenship regardless of you. One parent having permanent resident status would also be enough.
http://www8.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/aca2007254/s12.html
And beyond that, Australia has 2.8% foreign born population as compared to the US's 19.8. While those numbers aren't exactly the same as the number of non-citizen residents, clearly the impact of removing jus soli in the US would be far greater than removing it in Australia was.
I've looked around to see more of the justification used to remove jus soli from Australia law in 1984, and I haven't found much. I'd be curious what the reasoning was, and would not be surprised if there was some racism involved.