What's the salary of a senior dev in seattle? How much do electronics, appliances, cars and food cost?

Will that 700k USD house have wall insulation and double glazed windows and central heating?

I think there's a reason a huge chunk of skilled New Zealanders end up leaving.

In terms of affordability, you'd need to look at average salaries as well. My impression is that Auckland doesn't fare so well on that front.

Cities are defined differently in the US and New Zealand. That median in Seattle is for an area of ~80 square miles, whereas the median price for Auckland covers an area of 400 square miles. If you expanded the definition of Seattle to match, I'm pretty sure the median would go down (although it's interesting to consider whether Bellevue/Mercer/Medina would outweigh Renton/Kent/Tacoma there).

If its anything like Sydney, Australia then you should look at the quality of the houses too - not just the median house price. I remember looking at houses in Sydney and given the size, quality, and look they would cost half as much here in the Bay area. They can be tiny, tiny even for our standards and cost over 1 mil.