Your argument is something like, "If you want to have a successful startup, you should complete college, because most of these hyper-successful people have completed college."
You then say the probability of having a college degree, given that you are on the Forbes 400 list, is 85%. That doesn't necessarily tell you the answer the question "What is the probability of making it to the Forbes 400 list, given that you have (or don't have) a college degree?"
Let's think about what you are trying to do. You want to take the population of college attending startup founders (or future founders), and make a prediction about which members of that group will be hugely successful based on whether or not they complete college. Let's say you run a survey of your readers now and then follow up with them 10 years from now. This would allow you to calculate several things:
* The probability of great success with college completion.
* The probability of great success without college completion.
Do you think those numbers are going to be appreciable? Do you think they'll be similar in magnitude? I suspect they'd be much smaller than 1%. In other words, I don't think that college completion is a strong predictor of great (Forbes 400 level) success. You haven't really established a causal relationship between finishing college and becoming wildly successful.
I suspect (and I think this is the point the GP is making) that your last name (is it Walton? or Pritzker?) or your parents' income would be much stronger predictors of this type of success.