I don't think there are any rules for bathrooms other than those you noted. I have one bathroom that has only floor and tub/shower surround tiled. I am in the process of redoing it, and will keep the same amount of tile. our other bathroom is a sea of tile, floors, tub/shower walls and tile halfway up the entire wall all the way around. In my opinion the tile on the wall is a major pain because our ancient vanity is so dated, but can't swap it out because so much disruption of tile!