As an European, I'd like to add just a simple comment.
I think the whole thing starts with the livestyle in the U.S. Suburbia to be exact. The whole attitude towards the game is staged. It's like growing vegetables in a greenhouse. Someone said it before me, that soccer is an elitarian sport in the U.S. Soccer moms represent the more afluent in the American society. On the contrary - in Europe and South America it is the sport of the poor for the masses. The great thing about it is that you don't really need anything but a ball to play it.
I remember playing back home. My dad always bought me a ball and so I was the most popular kid in my condominium block. We played soccer every day after school. Just behind the block there was some patch of grass that we made our soccer field and played till dusk. I remember playing in 2 feet of snow. And it wasn't just me. Everywhere everyone played.
An American friend made a good comment once. "Do you know why Ronaldinho is better then the Americans?""Because when he was growing up he had 2 choices - play football or watch the monkeys climb threes in Brazil" Here kids have way too many other things to do - Playstation, MTV.
I watch some of my compatriots' kids who grew up here - they are nothing like when I was growing up - absolute vegetables. Becasue in order for them to do anything, their parents had to drive them, but they were too busy with work, so what could they do? Watch monkeys?