I'm no lawyer either. But I understand it to mean:
2D means an approach that only provides advisory or step-down information for the vertical profile; e.g. VOR, NDB, basic RNAV.
3D means an approach that provides vertical guidance from the IAF to the DA; e.g. ILS or some of the advanced RNP approaches.
In my personal thinking, if the procedure has a MAPt / MDA, it's the former. If a DA, it's the latter.
Fundamentally I think it's carefully written to provide future-proofing for the system. But, this being Australia, there are many pilots who would love to take CASA to AAT to exploit the slightest loophole, and many at CASA who would... but I need not finish that sentence. So it's been written by lawyers, for lawyers.
