I don't think they retconed Simon. Simon was almsot in diguise when he quitely sought passage about Serenity; the dark flasses and cloths, didn't even seem to fit his personallity, more like he was making a (lousey) attempt to hide.
And remember he was the one who made the suggestion of sneaking into a Alliance hospital and steal medicine. The show only lasted like 14 episodes -- we never really got to see all of his personallity.
Also remember, not getting paid very often, or eating very often, with a pissing, angry, conflicting crew, can kind of harden a person after living with them for over a year.