Probably they work fine, and this explains the reason of why they do not update it. About the drivers age, the last made from Prolific was at 2007. And probably in many other old modems that use IR communications like laptops or mobile phones. Currently this chip is also found on the Agilent USB -> IR modems. If the Prolific chip in your adapter is a fake copy, the driver does not work with it.
And the latest Prolific driver, it does one identity recognition at the hardware too. Even so the company gives their chips only to branded companies. Prolific (PL2303) adapter is an common solution about USB to Serial port adapters.
