If you visit other industrialized countries, many Americans are struck by how "dark" they are at night. I worked in Japan for a while, and although the business districts may be lit up like you see on TV or in movies, the residential neighborhoods are quite dimly lit compared to urban American neighborhoods and many parts are totally unlit. With so many people using public transit in Japan, there are certainly more people walking or riding bikes home from the train station in Japan, so Lono's point is well taken.

Or even when I lived in NYC, foot traffic definitely makes an area safer. Having bodegas open all night for people wanting to buy a pack of smokes or a snack or whatever certainly helps with the foot traffic, although all-night businesses in most parts of the US seem to just attract the "wrong" kind of crowd. I wouldn't want to hang out in many 7-11 parking lots late at night in many areas.