Regardless if there is a window or not. The idea of the exhaust being on a light is so that steam is exhausted to the outside when taking a shower (mold and mildew). The second reason to exhaust the odor. Like I said it is not in the NEC but is in the Building/Plumbing Code.
This is the 1st I have heard of this
I have never heard of it or been in any house or Apt where it is setup like this ?

Person stating it is in the same State as me - MA
Why would you want a fan on exhausting warm air in the middle of the winter if you are just brushing your teeth or hair ?