I assume Ted Cruz IS a natural born citizen.

[Jim Lane]

8. Obama "strangely" didn't make the argument you suggest because the argument is wrong.

From the Wikipedia article you cite:

Whether Obama having been born outside the U.S. would have invalidated his U.S. citizenship at birth is debated. Political commentator Andrew Malcolm, of the Los Angeles Times, wrote that Obama would still be eligible for the presidency, regardless of where he was born, because his mother was an American citizen, saying that Obama's mother "could have been on Mars when wee Barry emerged and he'd still be American."[62] A contrary view is promoted by UCLA Law Professor Eugene Volokh, who has said that in the hypothetical scenario that Obama was born outside the U.S., he would not be a natural-born citizen, since the then-applicable law would have required Obama's mother to have been in the U.S. at least "five years after the age of 14", but Ann Dunham was three months shy of her 19th birthday when Obama was born.[63]

Although the Constitution doesn't define who's a natural-born citizen, I think it's reasonable to say that it means a person who's a citizen as of his or her birth, without regard to anything that happens thereafter. That means you have to consider the law as it was in effect on the date of the child's birth. Although the law was later amended, to (IIRC) reduce and then eliminate the five-year residency requirement, that legislative change didn't retroactively confer citizenship on people who'd previously missed out on it. (If the change had been retroactive, then, IMO, such foreign-born children would have become citizens but still not natural-born citizens.)