Mark Zuckerberg and Priscilla Chan get all the press, but they're hardly Silicon Valley's only pair with ten figures between them. Dropbox's twentysomething CEO Drew Houston just became a billionaire — and we hear he didn't reach that milestone alone.

The problem with lists like BusinessWeek's collection of 13 under-30 entrepreneurs: Inevitably, in an effort to fill a demographic quota, editors scrape the bottom of the barrel. And presenting a balanced picture of these business novices cuts against the goal of serving up fresh faces. (Whether they're supposed to…