If you can even afford 20K you're in the top 10% of the US population. It's not a very big market, and even selling to that market is hard. Probably only 10% of that 10% will actually buy, and all of a sudden you're selling to 1%.
Selling to businesses is much easier, 99% of businesses can afford 200K if it replaces 3 x 70K humans.
Actually the high income households are becoming a greater and greater share of spending, referred to as the "K shaped" economy. For example, the top quintile of households accounts for about 40% of all consumer spending.
People in the US buy cars.
Can a household robot provide as much utility as a car? If "yes", the market gets pretty big.
Most people finance vehicles that cost much more than 20K.
I'd gladly pay or finance a robot that could have dishes clean, laundry folded, and carpets vacuumed by the time our family got home.
Your napkin math only shows that the market is identical. There's about 35m businesses operating in the US. So by selling to 10% of those you sell the exact same number of robots...