Considering that NZ PhD does not have course work, is it still considered equivalent to USA PhD degree? What are the job prospects (postdocs) in USA after getting PhD from NZ?
Rather than just look at the requirements for the PhD itself, you need to consider the entire educational system behind it. The reason for coursework in a US doctorate is that people can enter with only a BS/BA. And the bachelors degree win the US is a generalists, not a specialists degree, often with little research in it. The coursework is there to give a student the advanced knowledge they didn't get earlier and to prepare them for comps.
This is very different from the educational system in other countries. Often, the entry level PhD student has an MS/MA that contained that advanced knowledge and is just about ready for any qualifying exams. In such places, the PhD starts out with research, often enough dissertation directed research.
But they all end up in the same place: a qualified researcher with a deep knowledge of some narrow topic.
So, there should be no real disadvantage in moving between countries for those holding a PhD from a reputable institution. There will be a bit of cultural shock, of course.