Thanks for the link. Well, of course I just quoted a few examples without pretending it's legitimate piece of statistics, however, there hasn't been all that many world chess champions so far (and Botvinnik, Smyslov, Euwe, Karpov, belong in that category), and thus a few PhDs or successful intellectual careers is already enough to show that something clearly sets this bunch apart from the general public. You're less likely to find a plumber or a shelf-stacker in that bus (no disrespect for people in these professions). Whatever causes that is another matter. I agree with you that drive and dedication - and not necessarily some innate talents - could be the crucial factor in this.