Curious where you live that people don't speed. Here in Ohio you're expected to go 5 over at all times, people will tailgate and honk if you don't. 10% is lower than that at all but highway speeds
Australia (as an example) has hard speed limits. If you go over their speed limits by 1kph (kilometers), you can get a ticket and they put speeding cameras in abandoned prop cars on roads to catch speeders. I learned this from a coworker who moved here (Chicago) from Melbourne as he was remarking about driving on the highways here.