Having lived in several row-homes, those air-gaps have several benefits. They act as firebreaks for pests and rot, actual fires, and significantly reduce cross-unit noise. They also allow (perhaps minimal) natural light in through the side.
I can't express how much I wish my apartment had just 1 window on the shared interior wall. It would turn a lightless cave into perfection.
I wonder what the energy trade off would be. I would think proper insulation (and heat from natural sunlight in winter) could work out to be more efficient than having the lights on in the middle of the day.
A bedroom may be required to have a window (and a closet), but an office, dining room, or "bonus" room doesn't. Thus you have apartments or houses, where people sleep in offices, dining rooms, etc. Legislating this just causes people to work around it.
It has a window, it just on a side of the building that's in permanent shade. The view is worth it though, I can see ~15 miles from my porch since I'm on the side of a mountain (which causes the permanent shade since it wraps around ~270 degrees behind the building.
