Jettisoned,
This line about third party drives being unsupported is disingenuous at best. The gulf between what they're saying and what they're doing reveals an opening that, with enough pressure, should allow you to get what you want.
First of all, on the 1.7 update pages it states that the firmware itself is designed to allow users to utilize drives that support higher transfer speeds, while at the same time warns that these drives are unsupported. Unfortunately for Apple the existence of the firmware update itself negates the claim that Apple does not support these drives, as the update is designed to allow for the use of these drives. If they had not addressed the issue with the original firmware update to 1.7, maybe then they would have a legal footing re:lack of suppeort for user upgraded drives. But then...
Secondly, the simple fact is Apple does not sell internal hard drives from their website, yet their laptops include explicit instructions for upgrading the drive. This is another case in which Apple's stated policy of "not supporting third party drives" does not jive with its own actions.
When pressed, inconsistencies like these, should always be adjudicated to benefit the consumer. Push harder, go up the chain of command at the store level, district manager, regional manager, etc. Let them know the BBB and your state's Attorney General will be notified. Good luck!