tech
Without going around in circles, I strongly disagree that it's that simple. If you've come from a stable home life, with a good education and a decent work ethic then it's a lot easier than coming from a broken, abusive home where everyone you grow up around doesn't or has never worked. A child who grows up in that environment faces far more difficulties than someone who grows up in a leafy suburban middle class family. A warm bed, loving family and full stomach go along way.
That's not say it can't be done, but it's like saying the guy who starts with $10,000 can become a millionaire as easily as the guy who starts with $500k.
I disagree the guy in the middle class family doesn't really want for more. A good education and uni is a nice way of getting a good job. The majority are comfortable and their fear of losing what they have generally keep them comfortable. Those that come from nothing see what they are missing out on and have nothing to lose. Knowing you can survive on/with nothing is as good a motivator as any. I know a few that came from the worst conditions to make it between the $1-$50 mill range. I don't think its any easier for a guy from middle class.
As someone else mentioned a lot of the millionaires I have met don't come across as high IQ.