Are all employees internal customers?

Quote: “It is recognized in the marketing literature that all employees of an organisation are internal customers. [...] Internal customers generate goods and services for the end customer” [1] page 2

This description is remarkable advanced, because in the common understanding of leadership the employees tries to satisfy his boss. The customer sees his boss as a customer who gives him an order. But it seems, that the marketing literature and especially the newer one has a different understanding of how management is working. The idea is to flip the social roles. That means, the boss is trying to help the employees and the employees are helping the external customers.

This is called total customer orientation and it seems, that at least in the management literature it's the quasi standard of how to organize a modern business.

[1] Conduit, Jodie, and Felix T. Mavondo. "How critical is internal customer orientation to market orientation?." Journal of business research 51.1 (2001): 11-24.