We had foreign banks who advertised that as a strength and sent their profits to their countries. But when there was a crisis they said we are just a local bank with the same brand as a US bank and won't give the customers their savings back.
I don't know about orbiter but FlightGear uses JSBsim for flight dynamics modeling which can be very accurate and was even used at NASA.
You are correct that as space is not the primary use case for FG the shuttle developers had to start from scratch on many things.