I think the idea of dropping out of college fits in with the general startup mold. Startups are disruptive, they do not follow the traditional path of what's out there. Likewise, dropping out of college and leaving that safety net is certainly disruptive. It takes a special kind of person to do that. Also, it is unclear how many of these billionaires came from the world of tech startups, inherently more disruptive than say, finance.
"Some of the most common professions among the parents of American billionaires (for whom we could find the information) were engineer, accountant and small-business owner."
It seems to me that most of them had a safety net - their parents.
That's quite possible for a lot of people. I never deemed this an option at all though, I just wouldn't admit I couldn't do it.
I paid my bills, lived frugally (but happily) and basically just...lived on less than I made?
So, were these last few traits something my parents graciously bestowed upon me? Sadly, no.
My parents were frugal to a point, but not cheap. Budgeting wasn't something I really learned the concept of in depth, until I went out into the cold. Avoiding credit wasn't something my parents did, though they never abused it or amassed huge amounts of debt, and could always pay everything off (I didn't know or care about this at the time).
The thing my parents gave me was a longing for independence, success, and the knowledge that if there is ever something I need to learn, nothing stops me from learning it.
Sometimes, no matter which route a person chooses, they will succeed just because of their willpower, hardwork, sacrifice and perseverance.
Consequently I think money is wasted on studies like this, each individual finds their own path to success, even if similar.