i have a tattoo on my right foot, and stars on my hips.. all the others are above the waist... but, i have never heard of any such thing. circulation issues can become a problem... so, i guess they are just trying to cover themselves where they can. i did however have a problem with getting piercings before. I have my nose and upper lip (monroe) pierced but did them at home by friends who are piercers. when i tried to get my bellybutton done at a shop, i was refused twice because of my diabetes.
i assume the only reason they say none below the waist is because of poor circulation leading to delayed healing... but, that can really happen anywhere with a tattoo. so, if you want some below the waist, go to a different shop for those ;)