It appears that Obama is a natural born citizen, according to the definitions you provide above. He was born to a woman who was born in the U.S.
Not true. My cousin is an American Born woman who is married to an Eastern European and they live in France where he is employed as a lawyer. They met in the US. Her children are not natural born Americans. They are also not French citizens. They do carry both American and Estonian passports. At the age of 18 with the use of the passports and ticket stubs showing a total time spent in the US of 4 years they can declare their American citizenship. If they want French citizenship they have to apply for it at age 18. If they marry an American, then any children born to them in the future would be American but have to be born in the US to be Natural Born. If they marry a Frenchman or any other nationality, the 4 year requirement must be met for them to claim American citizenship for themselves. It is complicated according to my cousin. She should know, she has been in France now for about 10 years and has 4 kids.
I would certainly agree with you that the plural used in the OED example is ambiguous though some would argue that other sources make it clear that it is the father who is the one who conveys the citizenship.
It might surprise you, but I would be satisfied if the Supreme Court ruled that they are satisfied by evidence Obama produces that he was born to a US mother and that therefore he is a natural-born citizen under the meaning of the Constitution. I think it would be wrong, but I would be satisfied. I do not think it would be a good thing for this country if the issue is just ignored.
ML/NJ