Interesting thought, but if Americans want to win NCAA XC titles, they need to work and train harder. Don't blame it on the Africans. They are looking for a better life. Don't blame the universities...they are just looking to field the best teams possible while exemplifying a world view in not only helping Americans, but helping others, not matter what nationality, achieve a better life.
Africans going to college here are much more likely to give back and help improve the lives of people in their societies. We get our degrees, buy a house, have kids, etc...its all very "me" oriented. Plenty of Africans start programs and donate money back to people who really need it, so that other people can have a chance at a better life.
I have met several African's in my life, while in college and after, some were athletes, some were not. I can tell you that there isn't one of them I would ever say anything negative about. They are good people.