Stephens's personal appeal gets much of the credit for this, but she's also benefiting from good timing, given the dearth of top female tennis talent in the U.S., where it's been nearly a decade since someone not named "Williams" was exceptional. In fact, the cupboard of massively marketable American female stars from any sport is pretty bare. Skiing's Lindsey Vonn and soccer's Alex Morgan and Abby Wambach are terrific talents, but they don't compete on the biggest stages very often.