Why is it that the Southern Hemisphere rugby teams are so much better than the Northern ones?

I'll offer a different angle to the others - I think one reason behind it is the style they play at. Player skills are roughly the same - once you get to professional level in a sport, your going to be good regardless who you play for. But the style the SH teams play at is far more intense. The big 3 are used to the intensity as they always play against eachother and so its their default style, but when the NH teams play against the intense style of the SH teams - its too fast for their liking and they find it hard to get into the game - and because of that they end up getting thumped unless they impose their game on the SH team from the kick off - which England did against Australia 2/3weeks ago and won.