Nonsense

Speed limits are set by civil engineers using a whole host of scientific data, local ordinances, state laws, and FHA rules.

You're vastly overestimating the sophistication involved in speed limit setting. Look up the concept of 85th percentile speed for more information.

As a caveat, this doesn't apply to every country, but it certainly appears to for the U.S, given that multiple DOTs list it as the "common method for setting speed limits".