Intuitively that makes sense but I'm not sure if it's actually true. It's relatively easy to convince someone who would otherwise go into hedge funds to instead do a web startup with you. It's much more difficult, however, to convince that person to do a startup to the field of, say, ethnic pharmacology. That doesn't mean the hedge fund guy would necessarily make a bad partner for a web startup though. (Stereotypes about finance people aside.)

Also, I know pg says that not being able to find a cofounder after a certain point signals a lack of competence or a bad idea, which is generally of correct, but also realize that in some areas finding a cofounder is literally 10x harder than in others-- independent of the merits of the founder or the idea.