To be fair, there's a big difference between changing the config register and then booting a Cisco to selecting no config in the EXOS bootrom.
If you change the confreg, you can boot and get to the config with no password trivially with a 'show conf'; this isn't possible on EXOS - the switch will boot with a default config and there is no way to show the non-booted configuration.
I may be missing an attack vector here, and if so I apologise; but I still think that if someone has physical access to a device then you have a much harder job to secure it. I could, for example, de-solder the flash chips and read them directly if I have the switch - you'd notice that for sure, but you can't prevent that even with encryption because the keys would also have to be there, so the switch could decrypt the config on boot 🙂
Paul.