I don't know the correct answer, but perhaps it will be even more helpful to go through some ideas about the physics that goes into the answer.
Presumably what the people at Cornell were thinking was that in daytime, even on a clear day, the bluish sunlight scattered by the Earth's atmosphere makes a bright background, obscuring the stars and most planets. In the absence of an atmosphere, that background would be gone.
On the other hand, unless you make a point of dark-adapting your eyes and viewing through some tube that keeps out sunlight and moonlight, any light that you see reduces your sensitivity to dots of light, even if that background light doesn't immediately surround the dot.
Here on Earth we have some nice clear moonless dark night times, at least if you get away from human-generated light. The situation on the moon is different.
Due to tidal friction, the same side of the moon always faces the earth. Any astronauts camped on that side will always have the earth in view. Because the earth has much more area than the moon, earth-light on the moon is brighter than moonlight on the earth. Furthermore, the time when the side of the moon facing the earth has its night (facing away from the sun) is precisely the time when the side of the earth facing the moon is lit up by the sun. So unless the astronauts were to go at least toward the region where the earth wasn't directly overhead, they'd always have either a bright sun or a bright earth in their sky.
All those problems with background light could be overcome with the right sort of viewing screens, or camping at the right place and carefully choosing a viewing time, but perhaps no one bothered to do that. If somebody knows the answer more specifically, we'd love to hear about it.
p.s. It looks like Wikipedia tells more or less the same story I had above:http://en.wikipedia.org/wiki/Extraterrestrial_skies#The_Moon
(published on 04/30/11)