Actually, looking closer it just might be the British flag behind the US flag in those sitting pictures...
But in another picture, another rule seems to be broken: "The [Australian] flag should not be smaller than that of any other flag or ensign." The Australian flag seems to be smaller and in the lowest and most inferior position of the three foreign flags on Australian sovereign territory (the other flags being US, UK and France - the other countries to hold Grand Slam tournaments ).
The annoying thing about that site is that it complains about the US flag being on the ground, but dosn't acknoledge that the US flag was given improper prominance over the host nation's flag thus causing an offence to their soverignty (as well as three other countries flags touching the ground too).
It smacks of arrogent patriotism, not a genuine concern for the sanctity of national symbols.
Fortunatly, Australian's are pretty cool and wouldn't have been too bothered... probably wouldn't have even noticed.