Kevin,
Good to see you posting. I am now even farther from Australia than when we met. I think from the small sampling of what I have seen in Scotland, Australia, and New Zealand as compared to the US offerings I would think that the sheer volume of courses here would lend itself to the rankings seen as someone pointed out.
One thing that will effect this question is just what it is that one values in a golf course. Having been to Australia (once) and New Zealand (once) I know I have seen the courses I most desired to see. In the US and the UK I have a longer list of courses I would like to see. Now this could just be pure ignorance on my part as I am certainly not an authority, not even close, on Australia/NZ golf.
Courses I most want to see in UK: Machrihanish, Prestwick, Rye, St Enodoc, Perranporth, and at least a couple of dozen more.
Ireland: at least 6-10, Ballybunion, Royal County Down, etc..
US: Myopia, Kiawah Ocean, Cuscowilla, Shinnecock, Pinehurst, Chicago GC, Camargo, Monroe CC, Newport CC, Pine Valley, Seminole, Longshadow, Sebonack, Ballyneal, Black Mesa, Chambers Bay, etc... I could list at least a couple dozen more that I have already played.
I think there is a bit more depth here in the US, but I could certainly be wrong. There are many here who are much more well-travelled than I that I would love to hear from.
Thinking about it a bit more, I am thinking the best way to determine this is to think of yourself as a golfer with a lot of interest in and knowledge of golf course architecture (assume somehow this information is downloaded into your brain), but that you have never seen ANY of the courses that seem most intriguing to you. What would be your list of courses that you want to see?
One thing that certainly skews the rankings of courses is the emphasis placed on major championship golf courses. Given that 3 of 4 majors are played in the US it is pretty natural that most ranking lists would be weighted with US courses. I know my personal list would look much different because I am not so enamored of championship courses. Having seen me play, you know why.
Have a great summer down there.