http://sportsillustrated.cnn.com/magazine/specials/sportsman/archive/?eref=sihp
Unless I missed somebody, the only non-US winners since 1973 were Koss (shared with an American), Gretzky (in the NHL, which practically makes him an honorary American to SI), and at least one member of Athletes Who Care (Keino), who shared it with numerous Americans. I imagine Koss got it because they wanted Blair to get it, and then they figured they had to honor Koss if they honored Blair.
For Bolt to have won it, as a foreigner, and a track athlete, in a non-Olympic year, he would have had to run the 100m in about 7.50 and set the world record in the shot put.