I've only read this page, but no one has mentioned the ridiculously large pool of players growing in the USA. Relatively, far more kids here are involved in development programs, while, from what I've seen at least, in Italy the kids just kick the ball about in the streets. I trained with the juventus 1990 youth team when I was 12, and absolutely no question they were all much better than me, but the difference wasn't astronomical. Take aside the fact that they are the most select group of kids, Italy doesn't seem to have many players lying around. I might be wrong since my estimates are only made based on my own experiences, but when I went to a village in the alps last year, I was certainly the best player anywhere near the calcietto(excuse my spelling) court there, and here I'm only a bit above average.
Overtime, with the amount of money invested into our youth's most popular sport, it has to eventually go somewhere. This could explain the recent signings of several americans over to the EPL, though I think far more will be coming in the next few years. That said, I'm not claiming we'll surpass europe, but I don't think it's too hard to at least sufficiently raise the rather sad level of MLS from 5 years ago.