Shouldn't be too hard to clear up - even for you bloggs :-)
CTAFs are established wherever shown in AIP - ERSA, maps etc. When operating in a CTAF, monitor and transmit on the CTAF.
When no CTAF is established by AIP, monitor and transmit on 126.7 (as required by AIP). Good airmanship - as per CAAP is also to listen in and transmit intentions on area (in case Joe Bloggs (captains mate...) is flying past.
I suspect your confusion comes from the missing word 'frequency'
"Multicom: The frequency (126.7MHZ) used for broadcasts while operating to or from a non--towered aerodrome that does not have a discrete CTAF assigned."
An aerodrome can have a CTAF without having a discrete CTAF
frequency assigned. In this case - the Multicom and the CTAF are the same.
So, for your examples
- operating to a non-towered, non-CTAF airport with one radio - 126.7.
- operating to a non-towered, CTAF airport without a discrete CTAF (frequency) - 126.7
- operating to a non-towered, non-CTAF airport with two radios - 126.7 and Area
As for being told to bugger off - good airmanship also includes not clogging up airwaves when ATC needs them..... I would think that the CAAP is telling you to make a general broadcast on area when taxing or when 15nm (or so) out. Not to broadcast every leg.