It's tied to your PSN account, There's a menu option for the serial code that's tied to the account that made the transaction, as in if u bought it digital on ur JP account, you need to redeem it through the JP account, it errors out if you try to use your EN account. Which imo, already means there's some form of account detection already baked in for the codes to get around the piracy issue.Well at this point that is expected. Somehow a lot of publisher held back PC announcements as long as possible.
As for the code, I bet it's because of piracy although I don't know how they generate the codes for PS4 (the code that given to you after finishing story)
If "steam refund" was really an issue either, you could just make the game delay giving you the code for a few hours, and it's not like you're beating RPG mode in either difficulty in 2 hours anyway. I'm hoping the JP community bitches hard enough about this to make cygames implement some kind of work around, because this was a really dumb decision for the potential long tail of the game on PC.