Let me ask you this, if you were a division mgr and got demoted over fudging numbers, or something similar. Would you tell people that you lied and cheated, or would you tell people it was because performance was bad? Now, I'll be the first one to say that two different people that do the same thing can be treated differently because one has good numbers and one has bad numbers. However, usually the unethical issues is what ultimately gets them.
You may very well be right, but think about what you're saying. Compare it to hourly - as the union doesn't recognize production, when management wants to move or replace unproductive employees, it has to get creative. For example, in my building, an irreg driver with a reputation for being slow was recently pulled for not putting highlight tape on all six sides of each over 70. Meanwhile, most of the other irreg drivers don't put any tape on any package. Thus, it's very reasonable to say the irreg driver was pulled for his production, even though "officially" it was for faux reasoning.
One other thing I'll suggest is that at UPS, when an employee is disciplined, suspended, fired, demoted, whatever... the reasoning spreads like a wildfire. One thing I've always resented about UPS is that nothing stays private or discreet -- everybody soon leans about everything. And often, it fringes on people's privacy / HIPPA laws.