This document might shed some light...
http://www.icao.int/anb/aig/Taxonomy...censetypes.pdf
Seems that all of us (in qualifying aircraft types) are 'pilot in command' when in charge (even of only ourselves) and the differentiation is by license privileges.
It seems reasonable to refer to a 'pilot in command' as aircraft commander and I note that the AAIB do in their reports.
I would imagine that this common status has something to do with any commanders empowerment to override any other authority or disregard the rules of the air, when the safety of the aircraft requires this.
Nonetheless, I have no plans to invest in a band leaders outfit or add the title 'captain' to my business cards, I'll leave that to the professionals who have earned this honorific and stick to trying to keep the take off and landings columns equal in number.