You make some excellent points, and you're right about an argument currying example being perhaps more practical. On the other hand, if I start chasing practicality, I then end up wanting to input data to the closure (both as the closure variable and when calling it) from "somewhere else", which begins to increase the complexity of the example to the point where it distracts from the core intent of the test.

Maybe I just have a personal problem with setting arbitrary limits rather than following decisions to their logical extremes in a case like this.