one reason (in league) is the U20 league down here; the kids coming out of school can only play in this feeder league if they are in fulltime education or working; no specific training can be done between 9am and 4 pm; they get looked after by the club, but not getting $1000's/week at 18 before they have actually done something in the game to warrant it. It certainly means that they focus and don't get distracted by FHM girlfriends as much as some of the younger players do in the Barclay's Primadonna League, for example…
Also, there is the expectation to win. You know about it because there aren't 3 days until another game comes along and so you can't just 'move on'. The players know about the criticism they come under and so do something about it.
Further to that, less games at the apparent highest level overall are played so the players are fresher; not as much of a rush to get back for the next game in 2 days time or whatever. the season gentley builds up in intensity; a pre-season cup tournament in AFL for example, before the league starts, not trying to compete in 3 comps at once like ERC, Guinness Prem/Magners/French super 10 and the Anglo-Welsh/French Cup in Union, all of which end at the same time of year; basically the management of the seasons and competitions is much better for the players.
A good example is how the Aussie cricket team are a bit vulnerable at the moment. Becasue most of the big names went to IPL when usually they would have downtime and a rest period, suddnely there is talk of too much cricket being played and a need to protect the players from that etc.
Also, skills seem to be a bit more of a focus than the gym junky culture in the contact sports in Europe, just like Simon Shaw stated a few weeks back. being fit and strong to compete is one thing, but what is the point of winning that contest if you then can't execute once in possesion of the ball? This starts at kiddies level stuff; the schools cricket and various Footy codes is all about the skills, not the glory or the bosh factor.