Police can ticket you for going over the speed limit, anywhere, anytime. Not sure why that is a surprise to the OP. Some people attempt to use the defense that “everyone else was speeding, so the cop shouldn’t have picked on me.” But that just doesn’t work.
There is on most major roads an unwritten concept of the “real” speed limit, the one that is enforced. Cops won’t pull you over for doing 1 MPH over the limit, but may have guidelines to pull you over if you’re 10 over, or in “flagrant violation” which is a judgment call. Police departments are always trying to trade off budget and how much staff they have against where they will get the most bang for the enforcement buck, and getting people to drive 55 in a 55 is just a lost cause.
The psychology varies, IME. If a limit is set realistically high, people don’t feel the need to speed; sometimes there is a speeding culture that shows no awareness of the legal limit.
When I drove in Utah last year and the speed limit on the interstate was, I don’t remember, at least 75, I found very, very few drivers exceeding the speed limit by any significant amount. When I drove in France two years ago, I found speed limits much higher there than for comparable roads in the U.S., and speeding was rare. You didn’t *have *to speed, the speed limits made sense.
However, I drive on the Capital Beltway all the time. I would say at least 75% of traffic moves faster than 65, conditions permitting. The speed limit is 55, the *average *speed is well over 65, nobody blinks if you’re doing 70, and 75 is common. Occasionally I’ll see someone hitting 80 (sometimes even 85 but IMO that’s too dangerous for the road and traffic under nearly any conditions). I would guess that if the speed limit were raised or lowered by 10 MPH, it wouldn’t affect driving habits at all, unless vigorously enforced. It is rare IME to see anyone pulled over on the Beltway, and I have never seen parked police cars shooting radar.