You're over-thinking this. The point is simply that no matter how good the cryptography in a system is, if there are humans involved then you need to worry about human factors as well.
The easiest way to avoid the human factor is to get a scapegoat. You make it seem like someone else is responsible for, or knows about, the crypto or its data payload. They will then torture that individual indefinitely until they confess to something. It's better if they don't know you or anything about your scheme as that way it'll look like they're holding out a really long time on important information.
Then the only thing you need to worry about is that person dying, in which case the investigation continues. So similar to upping the number of rounds on PBKDF2 every year, you need a new scapegoat every year, or however long it takes them to break either the crypto or the scapegoat.
