Would make since. I was thinking about that at work yesterday. It would go to marrying the device to the system. I think the original xbox did it with their hard drives. I do not think that this is where keys to the entire system though.
Because if the drive failed and was sent back to sony for repairs they would have to unmarry the drive from the mother board which would be near impossible if the nand contained the keys... however if they had an interface to connect to it and reflash it then I really don't see why not.