I agree that it may be overkill for such a simple function, but the author (at least the original author, Brandon Rhodes) is drawing an analogy to more complex applications.

He uses such a simple example so that his idea that applies to much larger, more complex codebases can expressed in a presentation/article, not to argue that all such simple functions need this level of decoupling.

https://en.wikipedia.org/wiki/Straw_man#Steelmanning