I think it's possible to reach this situation without a cover-up culture.
Survey feedback can easily drift upwards: as a few people start scoring 'great' more often than necessary, everyone else needs to start scoring average workers as great to ensure they aren't left behind. Eventually anything less than perfection indicates total failure.
Oh yeah, HR is ridiculous. For example at my company, if your appraisal says you "meet expectations" that's not good enough; you are expected to exceed expectations. The paradox of this obviously eludes whoever is responsible for it.
At appraisal time, you pick 3 cow-orkers to give you "feedback". Everyone stitches this up with their mates; if you tried to be honest - because no-one's perfect - you'd effectively be punished by having the lowest score of your peers!
He was presented the results by HR and just about flipped. If he had known who had said what, someone might have lost their job. Not having someone to single out, he just all berated us together - not the sort of boss behavior the survey was supposed create. From then on, I went back to my usual method of marking everything "perfect" and leaving no feedback text.