UP - That's nice if you can build your company(s) without public funding/financing.
Bwoods 11 - I agree. They MADE their money from starting companies / cutting edge science. But most of them PRESERVE their wealth by stashing at least some of their fortune in T-bills. I read that in a financial publication a few years ago - Forbes, Fortune ..... one of those types, I don't remember which one. I think they use that money as a safety net in case of market crash, legal problems for their company, etc. Some of the folks mentioned in that article were the likes of the DuPonts, Kennedys, Vanderbilts, Morgans, Rockefellers, etc. Wealth building is one thing - wealth preservation is another.
I read a lot of Buffet's writings / comments. He has recently revealed that upon his death, a large % of his money will go into the Vanguard Total Stock Market Index fund for his wife and heirs, trusts, etc. That makes sense - extremely low fees and exposure to all sectors of the market. Cover all bases - and with tiny expenses ratio.