My friend's en-suites in their big house in USA are much like most en-suites - nice enough if you have the space but generally here in this country lots of houses don't have the space for a separate bath/shower room.
My DM in her Victorian house which has a huge attic (runs the entire length of the house and the length is very long) has easily got an en-suite in the attic bedroom which includes a bath and separate shower cubicle. She converted the box room into a dressing/en-suite shower room (no toilet) which leads onto the main bedroom. he also had an extension built though which means that the large spare bedroom now has a bathroom and she wanted that with a bath and shower cubicle.
She had the attic room and extension built separately though, and at one point there was a slight panic over how much of the box room she'd use for the staircase into the attic but it wasn't an issue in the end.
When she had a house valuation recently the estate agents said that with the main bathroom and 3 en-suites then that was a lot but that some larger families would like that and also the shower en-suite with no toilet was fine too. They also have a toilet on the ground floor so they have toilets with every bathroom apart from the shower room which is handy I suppose.