Americans prudish? no, we are not. one reason is you have to call it something, two, that is where the bathtub is. same for toilet, that's where the toilet is. it does not bother me either way. besides i do not necessarily use the toilet every time i go in, so maybe i feel more comfortable saying i'm going to the bathroom.
and about being embarrased, you just have to turn on the TV and see all the commercials about herpes medications, homorroids medications, etc, and you'll know that no, we are not embarrsed to talk about anything.
oh, another thing that comes to mind is that most Americans who own cats keep them indoors all the time, and the bathroom is where the litter box is kept, at least by most of the cat owners i know. i'm not sure how it is in the UK, but that's just how it is all over the US. they keep them indoors, mostly because people are at work for several hours a day, that way cats won't get lost or in cat fights with stray cats, or worse, get hit by a car, and killed, as it happened to one my cats.