Machines can eat petroleum and electricity like cows can eat grass. That's why we have symbiotic coexistence with both of them. If machines could only eat human food, there would be a lot less of them. For example, it takes two acres worth of land to make enough biodiesel annually to fill up an suv gas tank. Properly cultivated, that could feed a significant number of people.
Rich people are only rich because there are poorer people that are economically relevant. We all use dollars to buy food, money gives you the ability to have others do your bidding. It is just a social construct though, a convention.
Once humans are economically obsolete (Sam Altman plans to have OpenAI make super-human investment decisions, and I wouldn't be surprised to see Alpha Zero take an executive seat at Google in the coming years), human money becomes worthless to the industry, and even rich folks will be powerless.