Yes, it only boots from UBoot because that is the "security measure" taken by Hyperion.
But that's wrong. You're running in circles. It does not
only boot from UBoot. The Classic version, mystic device version and most likely also the Powervixxen/SharkPPC boot
without UBoot. So UBoot as a security measure is quite useless, since the only devices which actually use it are bought together with OS4.