I wonder what kind of royalities they still receive for that song? I suspect the money is long gone and it will take many, many years to get 5% of the total of what it has made.
Also note that this publisher didn't buy the rights until after the songwriter had died, nearly a decade after the original release of "Down Under." That's probably a factor in why the judgment was so low and not the 40%-60% the publisher requested.
Of course, I am just speculating as a layman...I know nothing of Australian law except what I read in news reports.