I think you've just hit the nail squarely on the head. I have a feeling that's why it bothers me so much.
I'm also really bothered by the fact that it would hardly affect the time taken to do the waxing (it's not as if she has magically lost half her body hair, or maybe she has and that's why they won't show her on camera), so the beautician's comment is really rather insulting.
Also, if I think about it, if my beautician ever said anything like that about me I'd be tempted to slap her. I'd certainly never go back to the salon. a) it's a remarkably personal comment to make considering that the relationship between beautician and client is strictly a business one, and b) it's just plain bitchy.