This is all about poor forecasting, pure and simple. Had this involved a 146 or any other of the myriad types that use Perth without autoland and YPEA also clamped, things could have been very different.
Captains can use commonsense and all the resources in the world, but if the forecast is wrong?
I hope the forecasters learn a good lesson from this, and/or QF puts a fuel-permitting alternate on Perth for dark arrivals, just as MMA had on YPPD and YPKA in the 70s because of the possibility of unforecast fog...