Well, if the winding road is self-policing because of self-preservation, why isn't the straightway? Sure, people will go 80km/h, even 90km/h, but why not, it's basically highway conditions.
In some sense, I don't really care who sets the speeds limits and who enforces them. The legislatve and bureaucratic tangle is so Gods damn dense from my point of view, I wouldn't even know who to blame. I'm not stupid enough to think the officer ticketing me in responsible for anything but what do I know, maybe the chief of police can say something to the mayor, like "hey, people going 80 on that highway-looking street isn't actually dangerous".
As always, it's easy to pass the "not my responsibility" or "it ain't desperately broke, no need to fix it" for government decision-makers.
Also, speeding tickets are the good old new tax.