I've witnessed motorists honk (i've done it myself) at other motorists blatantly running red lights or stop signs. I assume most motorists "discipline" cyclists because

1) Most motorists whom chastise cyclists probably don't believe you have a right to be on the road in the first place. I've been yelled at/aggressively honked at probably 50 times(?) since I started road biking in 10/07. In every instance I was simply there. Just me riding down the road as close as "practicable" to the edge of the roadway.
2) Cyclists are completely exposed. There is no bubble so cyclists are verbally approachable
3) Motorists get to yell at cyclists and drive away without any recourse