I think the problem is that the phrase 'natural-born' had a commonly understood usage and meaning back when the Constitution was written. It was commonly understood that if one were born of a male (then later upgraded to include the female) who were citizens of the same country, the child was naturally born a citizen of that country as well. But the phrase went out of use, so its meaning went out the window as well. I think if Madison, Jefferson, et.al., could have seen the mess that exists because of assuming the phrase would be known by later generations to be extremely disconcerting and would have labored to make the meaning crystal clear. Because of the Founders' worry that the President might hold divided loyalties, that is why they used the phrase 'natural-born' as a requirement to become President. As travel was more limited, they knew that if one's parents were from another country, that there would still be an attachment to the place - and that holds up even today. The problem today is that citizenship itself has lost its importance. So now, even if a President is the child of two US citizen parents, there can still be divided loyalties, or even a loyalty undivided as Obama's is.
Just as the identification of our form of government as a 'democracy' clumsily made by so many today (not understanding the differences between a democracy and a representative republic), what chance do such citizens today have of being able to understand the now archaic phrase 'natural-born'? The importance of citizenship and its hereditary inheritance has lost all meaning today, something the Founders could never have imagined. I agree this is a less than stellar on-point prima facie proof of a Constitutional definition for 'natural-born'. The Court still needs to rule on a firm definition, sooner rather than later as the more liberals become Justices, the more liberal the definition of 'natural-born' will be, without any understanding of historical meaning or intent. Obama is a prime example of someone who is historically ignorant, and he's not caught out on many of his historical gaffes and misstatements because no one else knows, either (and are much too lazy to verify; now if it were Cain who showed such ignorance or {rubbing hands gleefully together} Palin, well. 'harumph, harumph, harumph').