Riddle me this, why does an American-produced television show cost over 2 and a half times as much on DVD in America than it does in Australia (and the UK)?

Check this out:
Australia: Six Feet Under Season 5: $49.98AU (~$38US)
UK: Six Feet Under Season 5: £21.97 (~$41US)
America: Six Feet Under Season 5: $99.98US

I really, really do not understand this. Can someone who has a clue please explain to me?

There is a reason all four of my SFU seasons are region 4. :(

Update: Six Feet Under Complete Series on buy.com. They’re offering all 5 sets in one box for $194.86! What on earth? This just proves their pricing is ridiculous.