All Inmarsat satellites though the F-3 series have been in inclined orbits since beginning of life. This gives them extended on orbit lifetime. The beamwidth of the Inmarsat L band ground terminals is large enough that tracking isn't required. The gateway stations operate at C band with large antennas that require continuous step tracking. I don't know for sure if the F-4 satellites are inclined or not. This was a very clever use of available data for an unintended purpose.