Illumination of these exterior stairs are required by the building code. The 2003 IRC sect. R-303.6 says "Exterior stairways shall be provided with an artificial light source located in the immediate vicinity of the top landing of the stairway."
R-603.6.1 says "the illumination of exterior stairways shall be controlled from inside the dwelling."
EXCEPTION: "lights that are continuously illuminated or automatically controlled."

It's like smoke detectors. Required by the building code for electricians to install.