Most rich folks are self-made, full stop. Here's some data: http://www.benefitspro.com/2012/07/20/fidelity-finds-86-perc...
However, I think you're dead on with most of your points. Being self-employed is in the "necessary but nowhere near sufficient" category on the road to wealth. The vast majority of self-employed folks never get rich. The vast majority of them work harder and earn less than their employed counterparts (there's good data on this, but I'm too lazy to Google it).
Short answer: work hard. Be self-employed because it makes you happy and more satisfied, not because you want to get rich.