It's different because you can't verify the authenticity of the custom hand-rolled cipher. This is a request for the accused to produce the keys only, not to do the work of manually decoding.
It is literally the same as ordering me to tell them how to make sense of the unreadable data.
I'm not giving them a plaintext copy of something already existing elsewhere (assuming no unencrypted backups), but producing new information for them.
And unless you used FDE with full authentication (AEAD), which almost nobody does, there's nothing that says that this particular ciphertext represents the exact plaintext I've had at any given point in time.
With XTS mode (Truecrypt) you can cut and paste together different blocks from different ciphertexts under the same key for as long as they're in the right positions. Depending on how much you know about the computer and if you've got access to multiple backups, you can splice together something that even if it doesn't contain anything illegal, it would look suspicious and incriminating.
Consider for example LE getting your full file version history of a container from Dropbox.
And revealing the keys is a kind of testimony that you have had read/write access to the drive, and that it indeed is encrypted (not just random).
If he had a password hidden on Mt. Everest and demonstrated that to the court's satisfaction, and then cooperated with the court's order to reasonably assist in decryption (e.g., allowing the court access to the sherpa that routinely retrieves this key and enters it to decrypt his disks via some remote mechanism), I assume he would be considered compliant.
But if this were really how he obtains the password (and similar schemes of off-site passwords and accomplices aren't so outlandish in the case of servers which might require the keys on reboot a few times per year), how could he possibly defend himself from the contempt charge? It sickens me to imagine being in the same situation. If this isn't an instance of the cruel trilemma, I don't know what is =(
His case hinges on whether he can prove that the work necessary to decrypt the disks, which is understood to mean entering the keys which he remembers, is testimonial self-incrimination and thus illegal under the Fifth Amendment.
Believe it or not, most judges are aware of smartasses and are not required to accept "Well, I don't remember, and you can't prove that I do, so ha! You have to let me go now!" The evidence surely indicates that this man used his computer regularly, which necessarily required unlocking his disks, and that means that by all rational conclusions he is, or at least was, capable of complying with the order.
Until the court is fully convinced that he is no longer capable of complying, or until the order is dropped, modified, or stayed, Rawls will remain detained for his failure to comply.
Whether or not this is true is precisely the crux of the matter. Your comment echoes the government's position: Decrypting the hard disk is not equivalent to testimony, and is therefore not protected by the fifth.
The defence and EFF's amicus brief argue instead that we live in a world where our phones and computers are effectively an extension of ourselves, and asking to decrypt those is equivalent to forcing you to testify on your most intimate secrets, which is most certainly not kosher.
Well that is understandable but what if he burned the passwords just before he got arrested, heck he might even chewed them up and those are long gone. How would they find out? If he is a such dangerous child molester should they go full Sam L.Jackson Unthinkable style on him?