TL, my understanding is that the actual ILS signal is largely the same set up, just that the back up systems is what makes or breaks you for a CAT II or CAT III runway. If I recall correctly, Aussie airports lack the necessary processes to ensure that the equipment and power switches across to the secondary source within a particular time frame.
Having flown into both LHR in CAT II conditions and autolanding into most autoland permitted runways in Australia at everything down to and including CAT I weather (8 1/2 years on the 767 will do that to you), I can state without a shred of doubt that the only times I've had issues with the ILS signals is when the critical areas were not protected.