The two main “culprits” here? A proprietary 7-pin connector which will replace the industry-standard 4-pin connector, as the extra pins are there to connect a proprietary sensor, which incidentally is the second component in Apple-branded hard drives to the logic board.
OWC says that “From our testing we’ve found that removing this drive from the system, or even from that bay itself, causes the machine’s hard drive fans to spin at maximum speed and replacing the drive with any non-Apple original drive will result in the iMac failing the Apple Hardware Test (AHT).”
Planned obsolescence or freedom that was promised in 1984? You be the judge. Nothing – absolutely nothing escapes the control of Apple regardless of hardware or software – at least that is the perceived image that people get if stuff like this keeps up.