This might rub some people on HN the wrong way but what these people call "work" isn't really work in the sense of what most people consider work. They jet here and there, intervene wherever they want, and everybody listens to them all the time. They can cancel and postpone meetings as they wish, and so on and so forth. It's work in the same sense as buying another house is work -- you have to get together with lawyers and plenty of people but in the end these people all work for you and you can also change your mind and not buy it.
That's also the reason why these multi-billionaires never retire. They've retired from real work a long time ago.