Please don't consider this advice, as obviously it is a gamble/crapshoot, and worked fro some airlines it would appear may not for NZ.
But, every airline I have flown in the last 6 years or so has had such an advertised carry claim, and I have broken it every time by orders of magnitude without being challenged.
For instance, South African Airlines has the 7KG limit. I had ALL of my important camera gear in my normal luggage rolling carry on. Perhaps over 50 pounds of weight.
Likewise to Galapagos, etc..
But It sounds like NZ may be far more likely to actually enforce this rule, so not sure why it seems to be so ignored elsewhere.
Other airlines much more often have these little cages into which you must be able to fit your carry on, so DO NOT exceed the specified outer dimensions! This will get your bag checked.