The real money in all sports is marketability. Michael Jordan at no point in his career was he the highest paid player in the NBA and I am sure he didn't care becasue the money made from endorsements drwathed his NBA salary. There are some sports like gymnasatics and speed skating for example where there is very little money made from competing. Appllo Anton Ohno the speed skater has a net worth around 10 million dollars and the gymnast Gabby Douglas, has already made about 3 million dollars and she is just getting started. I bet Lolo Jones who has a never won an outdoor global championship has a higher networth than Asbel Kiprop the Olympic and WC 1500m champ. - You get the point.
Bolt, Sanya Richards, Tyson Gay, Allyson Felix, VCB, SAFB are all very rich compared to the top middle and long distance runners which are mostly African. Mo and Galen are doing quite well; it helps to be from a rich country. With out a doubt, the African dominance has depressed the earnings potential in distance ruuning. Geb actually made a lot of money, but he stuck around long enough for people to know his name and he had personility.