I've beat this drum for years, and Dan Grime sums it up perfectly in this article: http://www.trackandfieldnews.com/wp/?page_id=410One key paragraph from the article:
What does all this mean? If we are limited in the 10K by our 1500 meter ability, we are not going to see American men medal at 10,000 meters in the Olympics until we get 3:35 or faster 1500 meter athletes running the 10K. Unfortunately, American men consider themselves 1500 meter runners if they can run 3:40. Most of these athletes should probably be 10K runners or even marathoners. Many of our 800 runners should be running the 5 or 10K and even some of our 400 men should be running the 800 or 1500. We simply don’t have our athletes running the events they should.
I've always believed that if Geb had been American, he would have been "just" a 3:31 1500 guy rather than arguably the greatest 10,000 runner in history and marathon WR holder. What I've never understood is why that trend continues today.
Ryan Hall is a great example. He ran 3:42 for 1500 in high school, so of course he's a miler, right? Nope; he's a 59:42 half marathoner and 2:06 marathoner (one of the fastest ever at his age, African or non-African).
What I don't understand is why it continues to happen so frequently.