> where subways cost 1/20th of what they do today.

1) We are talking about reducing the cost of labor, not overall costs.

2) Your logic only applies in the micro, not on the macro. If the cost of producing one thing goes down while population keeps their purchasing power, then what you are saying would make sense. The whole point of the article is that accelerated automation can bring a scenario where the cost of producing "things" would go down, but the economically active population would shrink drastically.