If you examine that map carefully you'll see that fall lines are quite short. I had choice of Thredbo or Perisher on my one day of Oz skiing in July 1997 and chose Thredbo for its 2,000 vertical despite lesser acreage. http://www.thredbo.com.au/wp-content/up ... il-map.pdf
At that time of year it's not clear how much of Perisher's acreage would have been open.
Despite the moderate climate and terrain, the tree line in Australia is only 6,000 feet. So the top 500 vertical or so at both Thredbo and Perisher is above that.