I'm actually disgusted by mjeone's posts on that thread you linked to. Are they a serving police officer or someone who wants to be? Either way I hate to think there are police officers, or potential police officers, with that attitude.
I was once told by a police officer (disclaimer: this may have been his opinion) that the speed limit is the maximum speed you're legally allowed to do, not necessarily the safest speed and not the speed you have to do for the full length of that limit. He said it may not be safe to drive at the speed limit on some sections of the road and it's up to the driver to adjust their speed accordingly rather than have speed limit signs for every twist and turn, especially on rural roads.