well for one thing the US store probably excludes sales tax.
the NZ store includes GST at 15%. that brings the direct comparison to $999NZD.
furthermore, I beleive prices for apple goods are set at a point in time when they launch and apple hedge their currency risk at that time.
If the price for NZ was set in July last year (whihc I believe it was), when the exchange rate was 1.4 instead of the current 1.17, then $649USD (ex sales tax) gets you to $1044NZD (inc GST). Presumably the remaining ~$80 to get you to $1123 can be explained by the fact we are a different market, with far fewer people and a different competitive aspect.
You might aswell do the same calculation for everything sold here, the comparisons are the same with everything we buy..from food to consumables to electronics etc etc... A can of Gillett shaving gel costs USD$1.97, here they start around $6.99!
However I dont however believe in the common argument that NZ is at the arse end of the world, considering that most electronics are made in China, we are no further from China than the United States is from china. The main difference is that the US are likely purchase 100x container loads compared with NZ's 1-2 container loads... hence economies of scale.