We don’t know where they were born.

But more importantly these studies just prove out that the zip code you are born in is highly correlated to the socio-economic status of your parents. Which is the real predictor for future status.

That, on average, they would be worse off if they were born elsewhere. It's a predictor - nobody was suggesting that it's the only factor, or that it's deterministic.

They were born to the wrong parents. http://philip.greenspun.com/bg/ is a great read about the specific advantages that a trivial percentage of Americans enjoy

The first line of the article qualifies the title by adding [being born] "to white, well-off parents who lived in thriving communities and were able to send us to excellent schools."

Edit: NM, removed off-topic content