Those in the know, starting with Sir Alex Ferguson, say that the English leauge schedule is to blame. They simply play too much football. Yeah, they're young, but it's a matter of a Premiership player lets say playing 90% of 38 games, plus three domestic competittions, including the FA and Carabo Cup, no break during Christmas/New Years. Ferguson says they're "exhausted" both physically and mentally by the time of the customary June and July break - when the Euro and World Cups are traditionally played. Then they're asked to play for their nation.
I got no stats to back it up, but I'd put up some money that no player, english or not, who is in the premiership plays well in June and July.