There's a terrific post I'm linking to on Jalopnik about speed limit enforcement, I've read the whole thing, and all the comments..... there's a daily hazard for everyone who drives a vehicle being discussed and they have a lot of cool stories and info in this article about what states fine for speeding, where lots of tickets occur, etc etc.
I was just learning from Wayne about a CHP officer's Q and A on tickets. . . and since the speed limit here in San Diego is 65, and the amount of speeders is about 100% of everyone on the road, they have a situation to solve with logic... and here's what Wayne said to the best of my memory: fewer speeders over the 75mph range means a more viable target for cops... you can't pull over all speeders, so pull over the worst right? I buy that, it makes clear sense.
Also, if you pull over a person for less than 10MPH over (for example. if that is only one point on you license and you can do a online course and have that removed for a price) than why should a cop bother? If they only pull over the far fewer people who go 20 MPH over the limit, they can get many more of them, plus the fine is bigger, maybe even be able to write them up for reckless driving (way too far over the speed limit) and nail them for even more points against their license that they can't get removed off their license no matter what.
The summary? The faster they go, the fewer there are, and the more you can punish them.
IE: More job satisfaction? Perhaps. But it accurately gets the worst speeders ticketed instead of wasting time with all the 5 mph over drivers who drive just as well at 70 (legal in some states and is the limit once out of southern California) as they do at 65. So why bother with a million minnows when you can land a few whales?