You are probably right. In my experience, at the prices I have paid, there seems to be little relationship between quality of service and price - YMMV so do your research. Cici at Oriental Spa is one of the best out there but she charges regular prices. I wonder if there are elite level SWs who are experts in male psychology, who can figure a customer out and leave him in a state of awe? Or women who are extraordinarily sensual or charming or charismatic by nature?
As for average demand by race, again you are probably right - not saying I agree that it should be that way, but facts are facts. IRL attractive white women are high maintenance, but in the SW world their rarity makes them even more attractive. But there are a lot of niche markets - Asian spinners, curvy Latinas, exotic black women, obese white women, etc.