a lot of the messenger kids just aren't into it, either because they don't care or don't want to look like nerds. the weird thing is some people don't seem to learn from their mistakes. for example, a friend of mine was hit late at night by a car pulling in front of him while on the way to BC. a front light would have at least helped him out, but i still don't think he runs either. he also won't get rid of his helmet (which is damaged from the crash) because it is a discontinued champione du monde catlike.
a lot of it doesn't make sense, but then again, people are weird about self-preservation. it's a lot worse with bmx/skating kids though. some dude in a kelly green blazer and played out haircut told my friend riding his urban mtb to "ditch the helmet and get a 20 inch". my 14 year old brother fractured his skull when he was hit by a car on his bmx, but still doesn't think wearing a helmet is worth it.
i started off with no helmet and sometimes a rear blinky, but i've moved away from that. i like to ride at least a front and rear knog light, though i usually have a cateye el-410 front and a red blinky clipped to my bag as well. i also have 5 helmets, and i'm always wearing one... (road, xc, bmx, full face dh, and cheap road for winter).