MUST a detached pool house on a residential property be considered under the rules that apply to 'residences?'

After all, a bathroom in a commercial location, or a 'public' bathroom, are not required to have the receptacle.

Design factors: As a general principle I'm in favor of having a receptacle; they always turn out to be handy, often for the most unexpected reasons (think of how 'wheelchair ramps' have helped the UPS guy!). Yet ... bathroom ... pool ... pool equipment ... chlorine fums ... such a receptacle might be nothing but a maintenance headache.