To compare, LiteOn has its iHBS112 that initially did not support bus encryption, but a new "series" of firmware could be forced onto the hardware [no matter what series of FW the drive shipped with] and have support enabled. It sounds like it's the same thing going on here. And as far as I know, the 112 could be flashed with 312 firmware, which also has it enabled.
So it's pretty much firmware based, in these cases, especially since LG recycled its hardware in the same fashion LiteOn did. The thing is, no one ever really mentioned if it specifically worked, but I'm also not aware of anything which requires that capability to test.
EDIT: I was wrong; for the LiteOn drives at least, it requires a specific revision of hardware, and no revision of firmware enables it. This is according to software tools which report support of the feature, probably the same software you use. From the Plextor PX-LB950SA (rebadged LiteOn iHBS212) thread: