http://www.keyway.ca/jpg/samaria.jpg
We are in Ohio, USA, and here you dont need a good reason to sue.
What happened was bystander apathy, the most frustrating of sociologies quirks. It's a direct result of lazyness, apathy, and selfishness. The idea being "I dont have to, because someone else will". This line of though permiates every aspect of daily life, and is one of the main reasons that humans suck.
It's common, unless your a fucked up individual that feels honnored by being presented with the opportunity to help some one. Those of us who would stop are the fucked up minority.
Try it some time, show up 1/2 hour late for work, tell your boss "I stopped and helped a bleeding kid who was hit by a car". Most (51% or more) of your bosses will hold it against you. 90% will probably first ask "was it you that hit him?", assuming that no one would ever stop unless it directly effected them.