As you mention, an en suite master bathroom would be incredibly nice, and if we remodel, it's _the_ #1 non-negotiable item on the list. Private bathroom for us, 'clean'/separate bathroom for guests/visitors.
My sister lived in a 4/1 with an odd feature: a toilet on a wooden pedestal in the (full-size) basement. No wall around it, not even a curtain. Just sitting there in a corner.
As she put it "you only need it every once in awhile, but when you need that second toilet, you're REALLY GLAD you have it!
I don't find the proliferation of bathrooms/toilets in large houses surprising at all. If I lived in a 4000-5000sqft mansion, I might not mind a 2-3 minute walk to get to my bedroom at night, but I sure as hell don't want to have to do so every time I have to use the facilities. It simply makes sense to have a toilet and sink, at least, near the rooms you use regularly.