Balashon has an interesting post about the various terms used historically in Hebrew for 'bathroom'. The pattern he traces is of cyclical euphemization; every word for 'bathroom' eventually became taboo and a euphemism was substituted, which eventually became a neutral term, and then a vulgar one, and wound up being replaced.
English is equally squeamish about words for this - we discarded the term 'toilet' in the sense of bathroom, even though 'toilet' was originally a euphemism itself, because the term became associated with the crucial apparatus in the room rather than the room itself. In my Midwestern dialect of English, moreover, even 'bathroom' is considered slightly vulgar, and in polite company 'washroom' is usually substituted (but not 'restroom,' which can only refer to a public facility - a washroom can be in someone's house). My hunch is that 'bathroom' became taboo when the euphemism 'going to the bathroom' became detached from the room itself - my father has an example sentence in his first book about a dog going to the bathroom in the kitchen. Ah, Generative Semantics - if only all scholarship was so uninhibited!