An interesting question H, I guess the wings are meant to signify speed and reflected the brave and exciting world of flying of that time. Perhaps the most famous set of wings (

) are Bentley's, but of course they came much later than Morgan's. Aston Martin also has a winged logo, as did Invicta from memory and I think Lagonda.
Both BMW and Spyker had propeller logos, which also signify their aeronautical connection, though Bentley also started off making engines for planes.
Austin-Healey and Mini were much later users of wings and I know there are other marques, such as Chrysler who used wings, though they changed to a Penta logo!
I think the origins of the logo is a question that should be put to Charles (Morgan) and I'm sure Simon will do that when he returns from his hols.