The previous Airspace Policy Statement (2007?) did make some reference to adopting the U.S. NAS, but that was amended in the current one to state this below. For good obvious reasons.
The Government expects CASA to adopt international best practice in airspace administration. This includes adopting proven international systems that meet our airspace requirements. The Government's airspace strategy recognises that international airspace systems (such as the National Airspace System of the United States of America) include a range of characteristics that should be considered, and implemented as appropriate, by CASA.
And that airspace changes must follow due process:
37 The Government‟s airspace strategy, to be implemented by CASA, involves the adoption of a risk-based approach to determining Australia‟s future airspace needs.
38 The implementation of this strategy requires the identification of risks to aviation safety using both quantitative and qualitative analysis, and ultimately the safety judgment of CASA as the airspace regulator.
41 The airspace strategy requires transparency so that the aviation industry has clear insight into the way in which airspace administrative decisions will be developed, taken and implemented including industry and agency consultation. The strategy does however recognise there will be times when urgent decisions are required to meet a safety imperative.
43 The strategy does not pre-determine the adoption of a particular class of airspace before airspace risk reviews are completed, but rather requires that the determination of the class of airspace reflects the most appropriate safety outcome as determined by CASA after completion of these reviews and consistent with the Government‟s policy objectives.
I suspect that if the FAA had a blank sheet of paper, they wouldn't adopt E airspace in many current locations. Now that it is there it would be difficult to change without major objections from various parties.