You don't "get practice" doing an M&A or programming low latency embedded programming or managing other people's money without having proven you have the intellectual horsepower and willingness to dedicate yourself to that pursuit. A PhD or MBA are convenient signaling of that ability. And you need look no further than this site to see that in fact folks with MBA's and PhDs do understand important concepts about economics and markets that random jackasses off the street with "practice" or "street smarts" or "common sense" or whatever anti-intellectual label you want to use just don't have. Not only don't they understand the concepts, they don't even enough to know what they don't know about them. So no, PhDs and MBAs can't demand a salary (I sure hope it's a hell of a lot more than $5K a month, by the way!) simply because they have the degree, but it's pretty tough to demand that salary without one. It's a necessary but not sufficient condition, to put it in PhD speak.