Theres more than one reason why we ended up with McCain...
If we had Romney it would have been the same...
Just like Barry...
Romneys father was not born here either...
He was born in Mexico...
But because his parents were citizens, Romney is a natural born citizen. (Assuming he was born in the US, which I believe he was)
Romney's father was a citizen by law, because his parents were citizens, although his father was not natural born, because he was born outside the country, an unlike McCain, not while his father was in the service of the country. Romney's grandfather had established residency in Mexico, while McCain's parents were merely stationed outside the US proper.
The children of citizens born outside the country being citizens at birth has been part of US Immigration and Naturalization law since the very first one. In most (but not all) cases even having a single citizen parent will suffice, although that is more recent, and is subject to more, and frequently changing limitations. If Barry was born outside the country, and his parents were married, then he was not a citizen at birth. But if born in the country, he's a citizen by the terms of the 14th amendment, but still not a natural born one, unless he's lied about who his father was.