For one thing, the speed limit is intentionally set 5-10mph too low, specifically to make it easier to prove guilt when someone breaks the "real" speed limit.
https://en.wikipedia.org/wiki/Normalization_of_deviance
While it is true that many people do speed, that doesn't make their speeding "the real speed limit".
https://en.wikipedia.org/wiki/Normalization_of_deviance
While it is true that many people do speed, that doesn't make their speeding "the real speed limit".