Creamie,
Re. the vast areas of R airspace outside Australia's territorial limits, certainly Australia can make "rules" that govern Australian aircraft, provided they are not inconsistent with "local" rules.
Whether Australia can limit Australian aircraft operations in a class of airspace that has no legal validity, and where ICAO rules (not Australian) apply, is an interesting consideration.
But that is not the point. R airspace outside Australia's territorial limits has no legal validity, and is contrary to treaties, to which Australia is a signatory. Such airspace, in conformity with treaty obligations, should be promulgated as W, Warning.
A-Gs know this, DoD know this, Infrastructure knows this, many years ago, high level agreement was reached to conform with ICAO on this matter, but the "decision" got lost in the bureaucracy. Australia continues to thumb it nose at these treaties.
Tootle pip!!