As far as I've read, the wealth gap between black and white people in America (I don't know much about other minorities) has been slowly shrinking since the late 1800's, where it stagnated following a century of rapid shift after the civil war.

In fact, the gap has grown(a little) in the last 20 years.

The slow progress shows that new deal policies aided black and white people, with the civil rights movement further closing the divide. So yes, this ideal single-income lifestyle applies more to white folks, but both demographics have suffered from the stripping away of those policies, which was already happening before Reagan's evicerating reforms in the 80's.