Looks to me as if CASA is following the NAS policy. If you look at Page 7 of the NAS document (see
here) paragraph 2.5, it clearly states:
"
and if necessary, a difference lodged with ICAO with respect to VMC minima…
Class D procedures will be aligned to the FAA application.
While VFR aircraft in Class D airspace are subject to an airways clearance (ICAO Annex 11, App. 4), the clearance may be implicit as is current practice at GAAP Zones and in US Class D airspace.”
If, indeed, CASA is moving to NAS Class D I commend them. It will mean that the non-GAAP Class D towers will have simpler entry procedures and no need for a VFR departure call.
The frequency will be less cluttered at these airports, and safety will be improved.