That's only true if you're following the "build to flip" model. Many supposedly companies all around the world become successful businesses by focusing on a problem that is perhaps less ambitious, but makes money.
Absolutely not. There are many ways for a founder to get rich. Liquidity is just one of them. A pretty standard way is for the company to start issuing dividends. The founder is presumably a major shareholder, and so if a big dividend is issued, they'll get a big chunk of that.
Obviously if you've raised VC, then that won't work - though angels will probably be more understanding. So, the conclusion is, liquidity events are only necessary if you've raised VC money. So don't raise VC money if you don't have to.
