Well, there's no denying that the NEC crossed over into 'design' with the bath issue. Look at the way it developed:
First, they wanted them GFI protected. Prior to this, bath receptacles were - if present at all - often tacked on to any convenient circuit. Remember the plugs in the bases of the lights?
Well, with the GFI requirement extended to bathrooms, the result was that bathrooms were now put on the same circuit as the laundry room - the first place to require a GFI. Anything to avoid buying another $10 device.
With the advent of pistol-grip hair dryers, curling irons, etc., in the '70's, it was decided to require the bathrooms to not only be on their own circuits - there were plenty of service calls inspired by searching for the GFI - as well as the requirement that the circuit be a 20 amp circuit.
(Prior to the '70's, a 'hair dryer' was something that today would make you think of a haz-mat suit ... a little suitcase with a hose, and a cap that fit over the top of the head. Or, something you sat in, and had a 'helmet' lowered over you.)
Still, the code allows multiple baths to be on the same circuit. As a result, a recent McMansion I worked on had the bath circuit zipping all over the place, just to serve all five of the baths, on three levels of the house.
Personally, I'm not convinced that this was the best way to do things ... but it WAS code compliant.
