At some point all that employment is going to plateau for the people creating all the shit for people (arguably now, or in the next 20 years). To use the GP's point, if a machine replaces 3 workers (that only requires 1 worker for machine maintenance), then that leaves 2 people unemployed. And your point is spot on here too; those 2 displaced workers will generally have to find work in another industry (services), as all the ex-farmers and ex-factory workers have had to do in the last 100 years or so.
But at some point, what we refer to as "jobs" now are diminishing. The numbers of human laborers needed for general manufacturing or farming is at an all time low and generally sufficient for the population in developed countries. Look at how much stuff we have already; the demand for more luxuries isn't going to increase (at least, not as much as it will displace workers. We'll probably see some increase in services, but this will eventually plateau too.
I guess the point I was trying to get at, was what's considered a "job" (at least the GPs definition) will be scarcer at some point in history, and there aren't going to be replacement jobs. There's only so many doctors, nurses, dentists, assistants, other service jobs necessary to keep the population comfortable and happy, while the lion's share of production and transportation will be done by robots. Maybe we'll see people keeping themselves busy with more volunteering, creating art or music, playing sports, or just playing video games & socializing. But those aren't "jobs" by today's definition (maybe for the 0.1% of artists and athletes that can actually make a living at it). So yeah, maybe if we have a basic income and everyone can live somewhat comfortably on that, then we can redefine what those "jobs" are (I'd love to do this and just play / create music, personally). But there won't be enough of those jobs out there by today's definition.