Truth be told, Jeff's (Bezos) parents put mortgage on their house to invest in their sons business. Kind of far from rich parents in position or owning a mine.
One of the big factors for both Amazon and Microsoft was their timing in the market. They both got in at seemingly the ideal time to explode with the technology.
If either guy had come around a few years later with the exact same product/service, there would have been a lot more competition already in development.
And Buffett's dad was just a representative from Nebraska. If a representative from Nebraska passed you on the street, you wouldn't recognize him.
His dad "ran an investment company" in Omaha Nebraska, not NYC. It obviously helped Warren at the beginning, but he also learned how to invest from one of the best teachers ever.
These are just good reasons to help out your kids.
Nobody has the right to call themselves a "self-made billionaire". Those simply don't exist, every billionaire got help and exploited others to become a billionaire.