Realistically it is often a regulator requirement. The logic being, "why hire a zero time foreigner when we could hire zero time locals?" When an airline goes to the regulator/government to say we need experienced foreign pilots it doesn't look real good for them to hire zero time in type guys. Thus the 500 or 1000 hour requirement. In some cases that can be lowered if they still aren't getting the guys or there are no locals what so ever to fill the positions.
Typhoonpilot