agreeHM was fortunate that the Duke of Edinburgh took an interest in the private (and public) finances from an early date but even so I don't doubt that HM herself kept an eye on the books as any astute landowner with many disparate assets would. Merely surmising on my part but I'd imagine the private royal finances and spread of investments are somewhat more complex today than they would have been in 1952 and William will need some time to fully understand them. That's if he's interested of course, otherwise he could leave everything in the hands of advisers and accountants, although I'd like to think he's smarter than that.
In 1952 royal finances were more secure: they didn't pay taxes, didn't pay inheritance taxes (now they must deal about this), received expensive personal gifts (now gifts are part of Royal Collections) and so on.