Farming is a bogus example. Upping food production supported a population explosion which manned the factories of the industrial revolution. But there is no industry which needs that sort of manpower now -- there really is nowhere for all those people to go.
If a tiny population is involved in farming, more people could work to produce the manufactured goods. Now if a tiny population is involved in manufacturing, more people can work to selling them.
A few individuals think of a revolutionary idea (mass produced motor car, IBM PC, iPhone), and millions make money making them, selling them, making accessories / programs for them. A few individuals think of another revolutionary idea to replace some of these products, and resources get diverted there.
When 90% population was involved in food production, there was zero market for personal computers.
Until singularity, I don't see this stopping. People can move on to the "next great thing". Singularity, if managed well, could make machines our "slaves" and we could all be "happily retired". It can lead to bad outcomes, but we have a lot of time to plan it.