"If a cop doesn't look the other way in such a situation, is he really doing his job?"

I gues it depends on the situation and the persons involved.

Legally, the law is black and white, with no exceptions. But,unofficially, most enforcement folks apply tolerence levels to make up for varying circumstances - such as allowing a buffer for vehicle speeding. However, that is up to the enforcement persons discrertion. If you get a tough one, or are breaking the law at a point when enforcement is bent on sending out a strict message - you face the music. Some serious offences have little, or no, tolerence levels.