Second, they're both developed countries. I have a family, and I have a responsibility to ensure that they're in a relatively safe environment with access to the same quality of life they're used to here. I also need to be able to have relatively easy access to a technical job market. I could likely get a job working remotely, but it's much easier to know that I can get an actual job if push comes to shove.
Third, and perhaps most subjectively: they're closer to the parts of the world we find interesting and exciting. My wife is terribly interested in Japan, for instance, which is easier to visit from Oceania than from America (no time zone change). If I moved to Germany, for instance, I'm close to most of Europe. However, I have virtually no interest in travelling around Europe. I'm much more interested in visiting Southeast Asia, for example, or other places that are somewhat off the beaten track. This is entirely subjective, as I noted above, but it's a fact that needs to be kept in mind: we're discussing where bartonfink wants to live, not where every person on earth should live.
When it comes to choosing between Australia and New Zealand, my wife and I keep changing our minds. Australia certainly has a stronger job market and larger cities with all they bring, but New Zealand seems to have a more laid-back culture that suits both of us very well. Further, from what I've heard, life in New Zealand is cheaper than life in Australia, so some of our other dreams (e.g. a beachfront house) would be a little more approachable. That said, I think we need to get the hell down there and actually visit before too long.
As I said above, if Atlassian wrote me an e-mail next week and said "Barton, we dig what you do - can we pay for you to move out to Sydney by Christmas?" I'd be hard-pressed to turn that down. I'd probably need Mapquest to double my salary to push aside an opportunity like that, and it's not because I dislike Mapquest or am underpaid or anything: it's that moving abroad is very important to me because I want to feel like I live in a country because I choose to live there and not because I happened to be born there. The world is a book, and the man who does not travel only reads one page.