I really don't for sure how it works but I presume it's a matter of the software recognizing the brand, and perhaps model, of hard drive. I see it in the same vein as system reporting tools such as Belarc Advisor and Everest Home Edition being able to report the brand hard drive, processor, and other components. And, I see it in the same vein as system monitoring tools such as SpeedFan and CPUID, where the software detects certain hardware sensors.
So, in the case of hard-drive-maker-branded versions of Acronis, hardware recognition is the basis upon which the modified version only works with a particular brand of hard drive.