not sure how up to date this is - it was taken from the Lonely Planet website and they are usually pretty good

Visitor’s visa
Citizens of Australia don’t need a visa to visit NZ and can stay indefinitely (provided they have no criminal convictions).

UK citizens don’t need a visa either and can stay in the country for up to six months.

Citizens of another 56 countries that have visa-waiver agreements with NZ don’t need a visa for stays of up to three months, ......Nations in this group include Canada, France, Germany, Ireland, Japan, the Netherlands and the USA.

as you can see New Zealand has 58 countries with visa free access (including many of our top markets for visitors ) changing the rules to require these countries to have visas could have negative impact on our tourist industry , one of the biggest earners for New Zealand ( not to mention that NZ passport holders could lose the visa free access that they have to many of these countries )

Australia has only one country with visa free access - New Zealand