That's the whole point it shouldnt need to be 'enforced'. It's only because we are a country full of bogans that will try anything to get something they arent entitled to that we have problems, not even an issue in so many other countries.
It's so sad that in Australia, with so many people just unwilling to follow basic rules and apply common courtesy, they have to do things like put curtains or a rope as a further visual reminder what not to do, even after being advised via the PA. Just doesn't happen in most asian countries and...
Pfft very funny how it's always people like you, trying to get something they haven't paid for, who condone this kind of behaviour. Stay back in Y and use what you have paid for, I bet you are the kind of sad soul that sits at a lounge entrance begging to get in when you aren't entitled to.
This has been standard issue for so long I'm surprised you don't know about it, any airline not just qantas. Non flight of the original leg of a multi leg booking cancels subsequent legs
It's so sad it's almost up to us all to police this or ask cabin crew to due to the massive amount of bogans that will try to sneak every time and then just try to play dumb when challenged, if more people simply followed the rules the system would work. Taking half a seconds to read the signs...