Maisonneuve has a great article on why you should jaywalk (pdf). It's not rocket science really, cities with lots of pedestrian traffic have more pedestrians friendly environments, and drivers are more aware of pedestrians - so they can and should jaywalk to continuously promote the "pedestrian environment."

Here in New York City, my own particular "promotion" happens on Canal Street, where I purposely walk on the street and get in the way of traffic (not that I am the only person in the street, if you have ever been on Canal Street, you know that the sidewalks are ridiculously crowded and people are always walking in the curb lane). The New York City DOT and NYMTC have been studying the Canal Street corridor for a while, but the big problem with their studies is that they assume foremost that it should move lots of traffic through a crowded downtown city environment - Chinatown of all places especially. So, whenever I am down there I do my best to get in the way of automobile traffic. Maybe someday the powers that the will understand that New York is truly a walking city.