nowhere does it actually say that in the ANO. I'll stand corrected if you post the relevant link
Interestingly, if your Oz licence allowed to fly "out of sight of the surface" like most ICAO PPL's (e.g FAA) do, then you could do the same in the UK, whereas if you converted to a JAA PPL (or whatever it is these days) you would be limited to "in sight of the surface".
Is aero's and endorsement in Oz? In the UK there is no such endorsement, but if you are flying on the oz licence, then you may well be limited to no aero's unless you can get the endorsement, presumably by an Oz FI.
I wouldn't bother converting unless there is some good reason you need to.