I'm just trying to explain why the book says what it says. With your method, John, you are relying on the battery to be fully charged, so it takes little or no current at 14v. If it were partially discharged and taking significant charging current while you were checking the voltage, you could wind up with the regulator set too hot.
And the hidden gotcha here is that protecting the generator from putting out too much current is at least as important as protecting the battery from too much voltage. The battery will put up with being overcharged a lot longer than the generator will put up with too much current!
Long time ago (back in college), I was spending most of my disposable income on rebuilt generators, before finally learning that lesson. A dead battery is a lot better than a burned up generator! Of course, back then, I didn't have a workshop manual, nor the electrical training I eventually got in college. Someone told me I could have fewer dead batteries if I turned the voltage regulator up a bit, so that's what I did.