"Why can't I remove 'for test/evaluation purposes only'? I know I'm running an evaluation edition, I don't need it rubbed in my face."
This prevents unscrupulous OEMs from selling machines with the evaluation edition of the product instead of the retail version. (Yes, this has happened before. Many times.)
The "For test purposes only" tag prevents unscrupulous OEMs from selling machines with uncertified drivers. (Driver-cheating has been a big problem, especially video drivers, since... well... forever. Those of you who are gamers know all about driver cheating.) To install an uncertified driver without a warning prompt, you need to install the test root certificate. The presence of the test root certificate causes the "For test purposes only" tag to appear.
We have also had many cases of corporate customers (and technology reporters!) who have had machines expire because they had forgotten that they were running the evaluation edition. When the machines expire on them, they are stuck with thousands of machines that don't work. This makes them extremely upset.