I personally want to call bullsh&t on this. But it is making me think.
What jobs use a lot of people?
I cant see farming being reduced any further in the western world. AI might be able to help the farmer with planning and a few small things, but it's not going to replace them, or the pickers who harvest the fiddly crops (at least not until we have robots! And Robots with AI!!!). In the third world, I would suggest the reduction in workforce would come more from getting western levels of equipment, then anything AI can provide.
Mining in the west already has a massively reduced workforce, and apart from some very limited cases (driving machines underground perhaps), I cant see AI reducing the workload there. Again, in the third world AI wont help anywhere near as much as western levels of equipment and procedures.
In manufacturing, maybe AI could do somethings, but I mean that's so case specific. I work in Aerospace, we already use CNC machines, but you still need an operator to program the machines, put the material in, move the pieces between different machines, then when you come to assembly, there's no way an AI can do any of that sort of thing. As for the design side of things, every 10 years "Automated Design" in one form or another comes up as the new buzzword (Knowledge Based Engineering, Automated Design, AI Design)... It's never worked out beyond the simplest of simple things, because there is always individual requirements on every product that require a person to control the output (and usually rework a ton of stuff). I imagine it's no different on the tech side of things either.
In the service and hospitality industries, you're still going to need a cook to prepare the food in the restaurant. You're still going to need waiters, and bar staff. Actually that's not true, with Sushi trains, and coin (or note) operated drink machines. But even though staff are the biggest expense in a restaurant, restaurants still employ them, why? Because people like talking to a person. A few restaurants or stores might embrace robotics, etc. but again that's not AI, and it certainly wont be the majority for a long time.
So where could AI actually have a major effect? Advertising, Hollywood, Management? :P Would we notice if it took over those positions? Maybe it already has? ;)