> The US is a different world than most countries which tend to be geographically tight and culturally homogenous

So, if this was the issue, you'd probably expect outcomes to be better in less diverse, physically smaller US states. Looking at, say, life expectancy by state (https://commons.wikimedia.org/wiki/File:Life_expectancy_map_...) doesn't seem to bear this out, really; on your theory you'd probably expect, say, West Virgina to be handily beating California or Texas.

Also, of course, _Australia_, which started the thread, could hardly be called either geographically tight or culturally homogenous. Australia is roughly the size of the contiguous United States.