Go to my post at #6 for the link to the United States Citizenship and Immigration Service page concerning “Citizenship”.
There you will find the three types of legal, statutory citizenship recognized by the U.S. government. Natural born citizenship is not mentioned BECAUSE it is not a type of citizenship.
Natural born citizen is ONLY an eligibility requirement to be President of the United States per the U.S. Constitution, Article II.
As I told another FReeper, show me the clause in the constitution that requires this or show me the court case that defines Natural Born as having to have two citizen parents if you are born in one of the US states. In reality there would have to be an amendment to the constitution in order for this to be a requirement since the constitution specifically excludes the need of having Citizen parents if you are born in a US state. Read the constitution and understand it, it is your friend.