As I understand it, the MCA were offered the satphone option and jumped at it since it was new and, in theory, improved technology. However, the compatability with what presently exists at the ARRCK was either assumed or ignored.
Yes HF is old hat but it is the primary source of comms between the tasking authority and the helicopters - in hindsight it does seem foolish not to have included it in the S92 spec. A modern HF set can still provide very good comms with the ARCC - just a shame only our Mk3As have one.