The fact that Auckland does not grow much of New Zealand's grape harvest has mainly to do with the less than ideal agricultural setting. Much of the area is already inhabited, and they simply can't reserve more area for vineyards. Also, the weather is wet, which can be tough on vines and grapes. But Auckland does have some climate factors working in its favor. The amazing heat of the region does foster certain types of grapes, especially those used for red wines.
One of New Zealand's greatest advantages in wine making might be its latitude. Auckland and other parts of New Zealand are the Southern Hemisphere's equivalents to many of the originating countries of those who traveled to and settled in New Zealand in the 1800s [source: Cooper]. So although New Zealand presented new challenges and unique advantages, much of what the European settlers knew about winemaking was easily applied to the similar climate they found in New Zealand.
If things had been drastically different -- perhaps if they had to study the climate to understand what types of grapes would survive, or if grape cultivation and wine production were harder and more expensive for the settlers, they might have foregone transplanting and growing grapes in favor of simply importing wine from the European countries they left behind. However, the similar seasons, climates and conditions allowed the settlers to utilize their knowledge of viticulture in their new home.