I think its a bit of a jinx tbh. England have been way below what they should be. Johnny Wilkinson, who kicked the goal has been injured pretty much 80% of the time. Seems a bit wierd to me.
Theres a possibility that the players have slipped up somewhere, genuinely, and they think (in the back of their minds) that they have slim chances of retaining the cup, and therefore this is effecting them on the field.