Getting back on track a little bit, there are only a few companies that actually make laser printer engines. I can't name names, unfortunately (not that I don't want to), but it means that most laser printers, including color lasers, are going to be based off a limited number of printing engines. It might be worth the time to see if all the printers doing this are based off the same engine, or engines from the same company. That could help lead back to the reason why they started doing this in the first place.
I agree, BTW, that this is pretty scary. Being tracked by my printouts isn't my idea of privacy.