It would seem that the Performance Review is less a measurement to be taken accurately, and more a Tool to be used to subtly move people.

The study you cited provides a useful enumeration of why. And if you read carefully you can begin to see that the perception of the tool is likely to be incorrect. (that of a measurement to be taken accurately).

To quote the end of the study: " The goal then is not to arbitrarily and ruthlessly try to eliminate politics but, instead, to effectively manage the role politics plays in employee appraisal."