I heard this story too, when I became a manager and received some training from the HR director, at a F500 company. The idea that people are not motivated by money was drilled into us. Yet I became a manager so I could make more money. I formed a number of impressions:
0. A caveat about the "studies" is that they typically start with workers who are already receiving market compensation. That little bit is always left out during the seminars. At the factory where I once worked, unskilled workers quit over a $0.25 per hour raise offered by a nearby factory.
1. Most HR personnel have psychology degrees, so they are trained to believe that people are motivated by psychology. Imagine if HR people all had economics degrees. For me, treating my fellow workers as homo economicus is a sign of respect, because as engineers we are paid to make rational economic decisions.
2. It's a bargaining strategy, intended to attach a social stigma to people who demand more money, and to make the money game more stressful for people by making you feel like an oddball. This is also why people are discouraged from discussing salary from one another -- divide and conquer.
3. They are also bargaining with their managers, i.e., telling me as a manager that I shouldn't ask to pay my people more -- divide and conquer.
4. Yet... I looked around and the managers who had the highest regard and most power in the department, were coincidentally also taking care of their people with promotions within the ranks (e.g., from junior to middle to senior), meaning that they played the salary game differently than what HR told us. In addition, because salary budgets for the work site are relatively inflexible, it's kind of a zero sum game, and more money for their employees meant less money for mine. I was competing with the other managers for salary budget.
5. I decided to compete hard. I somehow convinced my higher-up that my people were "special" and thus immune from stack ranking. This eliminated the zero percent raise in my group. I got one engineer a nice raise. I promoted two others, making them equal to me in rank. In practical terms, a promotion in between annual review cycles was a way to give someone a raise, since the money came out of a different pot. This kind of thing worked for a few years, then I started to run out of luck, and stopped being a manager.
The people who I took care of are now some of the most valued and loyal employees.