I think you might have a mistaken idea of how precise such guidelines can be. There are always border cases and exceptions. Trying to nail them down completely makes them complicated, which only generates more border cases and exceptions, not to mention the literalistic sort of objections that only consume time and generate even more objections.

That's why both the HN guidelines and that Who Is Hiring rule are written in simple language that gets the bulk of the point—the spirit of the law—across, without pretending that there isn't still room for interpretation. Readers are expected to interpret them reasonably, and in practice this works just fine. Sometimes they interpret them differently from how we do, and then we try to explain better, on a case by case basis. It's ad hoc and imprecise, which is exactly how something as messy as a large internet forum needs to operate.