J52, I've travelled extensively in Asia, Europe and North America and I've never been asked to prove my bag was mine by producing a bag tag so this isn't just a problem at Sydney International as you say. It is unfortunate that someone tried to steal your bag, but sadly, there are mischieveous individuals everywhere trying to take advantage of others.
The best lesson you can probably learn from this is to not pack anything you can't afford to lose in a checked bag, and have travel insurance for the things that can be replaced if lost or stolen.
Bad things happen everywhere, not just Sydney.
But well done for being alert enough to stop the thief before it was too late!!