I don't think the sports analogy serves their argument (and I'm not sure I really see what they do all that differently than YC). I don't know Michelle Kwan's story, but of the other three they mention: Ichiro got a nice 17M/year contract. Nash has a couple of MVPs and was the 15th overall pick in the draft. Iverson was a number one draft pick and led the NBA in scoring several times. Ichiro came from Japan instead of the traditional draft/Latin America -> minor leagues route, but considering the Mariners paid $13M just for the rights to negotiate with him, he wasn't exactly an ugly duckling by the time he came over.

Really, all those guys are more like a phenomenally successful startup than not. There are countless prospects in sports—this is most obvious in baseball with the huge minor league pro leagues, in basketball the NCAA serves a similar role—and only a very, very few of those players turn out to be stars. And frequently scouting for them in advance (like at the HS level) is a crapshoot. If you were an up-and-coming agent and happened to land a Nash, Ichiro, or Iverson, he'd likely be worth more to you than all your other clients combined.