"Suitable Airport" is not open to interpretation at all. It is Black in white, at least in Air NZ's manuals. A suitable airport is an "Adequate Airport" (essentially, long enough and strong enough), with weather, atc, and approaches that will allow a safe landing to be carried out on the day. The only real reason to fly to a more distant suitable airport is if the Captain believes it will be safer for some reason. That reason would not include pax convenience, engineering support or a nicer cafe for lunch. Also, it is nearest in terms of time, so if you were at 30 000' over Hamilton, you could argue that Auckland is just as close in terms of time.
As for the stories of "plummeting to our deaths", what else can we expect.