I wondered about this too. My skin happens to be almost exactly 18% so no problem taking a shot of myself but....

Assuming everything around the subject is not extremely bright or dark, is there anything wrong with metering person's skin and put it on zone V where most detail can be captured? On the same token, knowing the difference between white skin and black skin from zone V is only one stop on each side, is it that important that we compensate for this?

I think the darkest of the dark skin and lightest of light skin can vary as much as 2 stops from zone V. In such cases, do we still measure zone V or split the difference?