The law applies to budget, income tax or population figures as well as street addresses of people listed in the book American Men of Science . In the face of such universality of the law, it's quite astonishing that there exists a more general framework - Zipf's Law . Which, in turn, falls under a more general rubric of scaling phenomena. Strange as it sounds, Benford's Law may be explained from the first principles, the chief among which is sheer universality of mathematics. The size of a river basin is a function of the river's depth and breadth.
Functional dependencies are abound.
This is why studying Calculus makes so much sense. But the notion of function does not reduce to a functional relation. The latter observation is very important in understanding the origins of Benford's Law. For example, statistical data on river basins will probably not include streams below a certain size. At the other extreme, there is a natural upper limit on the breadth of a water conduit after which it's more reasonable to talk of lakes, bays, seas, or oceans.