If the site had stated that they were modified PC drives to fit the A1200/A600... would that have stop you from ordering the drives? I would then have assumed that they were modified to be a 100% replacement. But, as stated before, if you've got special kit the drive has to be fitted into (the Infinitv tower is special) then it would have never hurt to have asked.
You should compare this situation with something like this:
Say, you own a Skoda Fabia like this one
edit: oversized image, will shrink itedit: shrinkedand let's assume you damage one of those Lexus-look rear-lights. Now, you call the local Skoda dealer and ask for a replacement rear-light of your Skoda Fabia. He politely askes for the year of built, if it's a left or right unit and within a few days you get what you asked. Only to find out that it is the bog-standard version he send you. Can you blame the dealer for delivering the standard version?