Part of my opinion is that we are all built differently and should not deviate too much from how we run naturally. At the same time, I think there's some value in working on your mechanics.
But to suggest that this is the reason Americans aren't reaching their running potential is extremely simple minded. I don't care how good your form is, if you haven't put in effective training to condition yourself, you aren't going to be very good. Whereas, I think the opposite can be true. One example is Paula Radcliffe whose form is very different from the supposed textbook form (she has a high arm swing, bobbing head) but who owns one of the most dominant world records in running. Maybe Paula could run even faster with "better" form, but probably not (IMHO).
If you want some really insightful discussion on this topic, I recommend the Sports Scientists blog.
http://www.sportsscientists.com/2008/01/running-technique.html They also have a great book that covers this and other topics.