Well... I'm just guessing and may be way off. If you run the PSID, you can then format the entire drive. In doing so, the encryption is lost and therefore the data is not in a usable state but.... the data is there. So to most of us, running the PSID Revert is just as good as wiping the drive but hand that drive to the right person and the data could probably be unencrypted much easier.
Just a guess and again, I could be way off. I didn't feel like reading but felt like posting.