Hi Steve
I believe that the AirNav philosophy is that because a particular airframe may be used by different operators (on leases, etc) that linking a logo to a Mode-S code would not be a good idea, because most of us would rather see who the aircraft is flying for on the particular flight. I agree with you though, that it does leave some gaps.
Perhaps a fallback where, if there is no Flight ID, the Mode-S code could be used, might be possible in the future.
Rod