I think the 'black people better at running' thing is probably to do with climate and altitude. If you run in hot, horrible conditions you get really fucking robust against heat and discomfort, so when you come to the UK, a chill-paradise by comparisson, you'll have been conditioned to cope so much better in easier climates.
It's also a fairly well known fact that the ideal way to train for running is at high altitute, as there's less oxygen. This makes you blood cells a shitload more efficient at carrying oxygen. Obviously, if everyone trains and races at high altitute, there's no net gain, however if you live high up, and condition your body into an oxygen-efecant machine, when you come down from your mountain to race with the rest of us, you've got a massive advantage. The higher concentration of oxygen gives your muscles power++.
This is why Paula Radcliffe doesn't live in the UK. She lives on the top of a mountain in a foreign country somewhere. Trufax.