I think it's just the difference between the unreasonable goy in front and the normal, reasonable people behind them. There's so much buildup in the 3 minutes it takes them to work out that yes, they have 6 feet to spare in passing you that it seems as though the next person is right on your bars, when in reality they just understand that they can't do much to help if you decide to swerve into the middle of the lane for fun when there's a car there.

City riding is this 90% of the time. I guess there are more morons riding through downtown cores than out on the real routes, though.