Sorry but Apple's policy has been for a while to allow end-users to upgrade their HDD and RAM without breaking any warranty. This is prescribed by Apple, and guides are provided in their support page.
Even Genius Bar employes guide customers through the procedure (depending on the Store).
Unfortunately this is not a simple incompatibility problem, but a severe bug in the chipset design by NVIDIA, indeed a bug I've seen in all NVIDIA SATA controllers from the nForce 4.
All manufacturers do have bugs, it's usual, normal, expected, Apple is not free from errors, they are humans.
But here the problem is indeed NVIDIA, that has Macintosh users quite used to bugs.
The ONLY way to upgrade the hard disk, unluckily, is to force it to the slower 1.5 Gbps link. Even using an Apple certified drive will fail if the disk is not forced (like for example, requesting a newer drive shared by another MBP model).
Saying this is a rumor it's more politics than technical truth.
Regards,
Natalia Portillo
Apple Certified Macintosh Technician