We had this discussion here a few months ago. I suggested that the reason American airlines' services suck is quite simple; for Americans, air travel is no longer a luxury activity, it has become a necessity, quite like taking a bus.
Here in Europe, air travel is still seen as a bit of a luxury. When you want to travel to another country or city, the first place you call is the state railway. In the U.S., distances are greater and the rail network far less developed than Europe's, so therefore the first call goes to the local travel agency. Because there're so many airlines, and the competition so stiff, airlines will cut services in order to offer the cheapest ticket. Americans are interested in the cheapest ticket, not the best service.
Also, remember that in the U.S. there is no national carrier. There are no state subsidies and no national reputation to maintain. Compare this to Europe where every country takes much pride in their national airline. Many are still at least partly state owned and subsidized. They can afford to spend more to maintain higher service standards without having to answer to angry shareholders. In the U.S., it's a pure capitalist free market in force - he who makes the most bucks while outdoing their rivals stays in business. For those who don't, no matter how mighty, how proud, how many 747's they fly, (we take a moment here to remember PanAm, Eastern, TWA and the countless others) simply go belly up. There is no government rescue, no saving grace, no pity.
In Europe, your typical 2 hour flight usually crosses over half a dozen different countries, therefore, most flights are international. International flights, by their nature, HAVE to have higher standards, customers have higher expectations. In the U.S., you can fly 8 hours and still be on a domestic flight in the same country.
Unfortunately, I don't know enough to comment on Australia/New Zeeland, but I can bet it has to do with you guys not having as many carriers and competition as the U.S.