It's like a recent Canon digital camera that comes in two versions, the profesional and a consumer, with the pro going for around $500 more. But if you get the consumer version and get a hack for the firmware it now has most of the functionality of the pro version.
And related to ATI is the recent hard mod to get an ATI X800 to a ATI X800XT which is $200 more. Seems to work with a certain series of serial numbers on the GPU. If the one you have is in that range there is a good chance you can hard mod and flash the bios with the XT bios and bang new card.
It goes with what you said. It's cheaper for them to just produce one or two variations of a board then just disable certain pathways etc.
Helps to keep cost down for them and us in the long run but we might just end up shooting ourselves in the foot if the manufactures of different products have to start producing different electronic boards for every make and model. Doubt that will happen though.
 
I still haven't had the nerve to check the serial number on my X800 yet.
 
S