I think it has to do with familiarity. That is how modern people think of floorplans. Really a similar thing can be said about hallways. In most buildings there were no hallways, just adjoining rooms. Where there were hallways they were primarily a way for servants to get from place to place without being seen.
Back to privies, with indoor plumbing it is easier to forget about that aspect "real life". Chamber pots just bring up all sorts of "realities" that my players usually did not want to have to deal with.
That being said, I usually leave them out of anything but castles or cultures that have indoor plumbing.
I often get a little extravagant with my windows too, medeival structures usually had very few, very small windows, for heating, defense and cost reasons.
Well theres a bit more than my 5 cents on the topic