Out of all the people that you know in one environment, eg: school, work, etc, only a handful would fall into the category of non average body structure. One or two chubby people, a few short, a few tall, but that would still leave at least 75% that would fall under the average body design. So in reality if you we're to describe them you would have to be very precise and it would probably be a little too excessive. 

Same goes for RP. Most people are assumed to be of an average body structure and only when you describe it would people notice the difference. So until then I assume that it's not listed simply because there is no apparent need to.