There's not really that much difference between AU and NZ, though it is weird to see that PNG requires a visa for AU, given that AU gives PNG a chunk of aid money.

You're right, there isn't, at least not in this nicely quantified way. Anecdotally, I've been treated much nicer on my NZ passport than my Australian one, even to the same countries (especially France, which I found curious).

Other Kiwis I know have reported receiving great treatment in France. Some have pointed out that they still feel a bit guilty about this https://en.wikipedia.org/wiki/Sinking_of_the_Rainbow_Warrior