No, it isn't hard to grasp, but you certainly need more information than you currently have to grasp it properly.
Cruz is exactly like Aldo Mario Bellei. Had he remained outside of the United States, he could have had his citizenship stripped from him, exactly the way Aldo Mario Bellei had his citizenship stripped from him.
http://en.wikipedia.org/wiki/Rogers_v._Bellei
Do you think a "natural born citizen" could have his citizenship stripped away for not living here?
No? There's the difference.
Wait, didn’t you just mock the Supreme Court for ruling that blacks were property. Now you cite some obscure case that does not define “natural born citizen.”
It’s all conjecture.
NO COURT IN THE LAND WOULD RULE CRUZ OR RUBIO INELIGIBLE.