Here's probably more than you care to read on this topic. I just finished it this morning: http://michaelochurch.wordpress.com/2013/04/16/gervais-macle...

The short version, as pertains to what you experience, is that companies have (since Enron made it fashionable) included performance reviews in the transfer packet as a way of enabling managerial extortion (for the sake of project expediency, although it's unclear that it achieves that) and passive firing, reducing lawsuit risk. The passive-firing infrastructure is supposed to be there to make low-performers look objectively unwanted (lawsuit issues) but the headcount limitations and transfer blocks actually end up getting used against high-perfomers that their managers want to keep captive. Google (which has Enron-style performance reviews) has a well-documented problem with this.