Folks,
The BIG PICTURE of the "why" of a 30 minute fixed final reserve is ---- that you actually have some fuel left in tanks on landing.
What too many of you seem to not understand or want to understand is that various errors can be cumulative, so that a calculated/indicated fixed final reserve may or may not actually be in the tanks.
You may or may not, in the real world, have 30 minutes endurance remaining.
ICAO didn't pull this one out of thin air, it is the result of a serious of fuel exhaustion or near exhaustion accidents/incidents over many years.
Without the need for "regulation", most major airlines adopted a FFR of 30 minutes thirty or more years ago.
If you want to criticize on this one, criticize CASA for:
(1) Taking this long (thirty years or more) to catch up, and;
(2) Making little or no effective attempt to explain, by effective education (assuming anybody in CASA understands the rational for the ICAO requirement) why the concept of 30 minutes FFR makes a serious contribution to air safety.
Tootle pip!!