a Jetstar flight advised ATC they were going to fly the VOR approach and then proceded on down the RNP approach
Not true
How did ATC bring themselves to let them Taxi or T/O?
ATC was on watch but do not make the go or no go decision with reference to weather. Weather information is given and it is up to the pilot to decide whether or not the required minima exists.
There is no requirement in the AIP for flights to be airborne 30min prior to ECT.