Sounds like the powers that be in your situation could corrupt any system.
Agreed. What happened here is that narag's employer wanted to fire him, or at least demote him. Irrespective of the moral issues, it's not at all unusual for an employer to choose their favorite customer-facing employees based on who their customers prefer. That's just good business. The review thing was just paperwork, basically. They needed to push some numbers around to get the result they wanted, so they did. Is that ethical? Probably not. But it's not insane either.
Well, I would say that the previous customer that I worked for during many months was very satisfied, so was my direct boss. They didn't want to fire me anyway, just to freeze my salary.
My point (same as in the article) is that performance is not the question, but market forces. It turns out they really lacked the power to give me a bad review. The same person that ordered the good review to be burnt and wrote a new one (very bad, I guess) was a few days later offering me 10% more pay, just because I was leaving.
My boss was asked to burn the review. Someone else from above would write a new one. I guessed what was going on (later my boss confirmed my guesses), so I didn't waste a second. A week later I gave the two weeks notice to go to a place with 20% more pay. I wouldn't if not for the review system.