I spent a few days in Singapore, long ago. I felt slightly anxious, but mostly because I wasn't familiar with the rules. I'm confident that, if I spent a year or two there, I would quickly become far less anxious than in other places--because the rules are so clear and consistently enforced. The less of a judgement call is involved, the less there is to be uncertain about.
Think about it: Is it better to have a posted speed limit of 65mph and a real speed limit of 75mph, and you just have to learn from experience where the real limit is? Or is it better to post 75mph and fine any driver as soon as they exceed it?
The point of poster a lower speed limit than what is applied is because both the sensors used by the police and in your card are inaccurate and it's unreasonable to constantly fine people who thought (and perhaps even were) within the limit.
And this applies to most other laws too - we can't expect everyone to know all the edge cases so some leniency for honest mistakes is needed.
Think about it: Is it better to have a posted speed limit of 65mph and a real speed limit of 75mph, and you just have to learn from experience where the real limit is? Or is it better to post 75mph and fine any driver as soon as they exceed it?