Our receptionist is not young and thin, she is attractive however. She receives people very well, and knows our frankly incomprehensible (to me) phone system inside out.
I do see Bonsior's point about not wanting to buy face cream off a 17 year old boy. I often think that when you see an anti aging cream being advertised by model who looks about 10.
There are positions where how you look is important. I wouldn't use a personal trainer who was fat or get my hair done by someone with crap hair.
It is complicated, but there are laws to make sure people/corporations are not just being shits as well.