Barack Obama identifies himself as black, Bob Herbert didn't invent that. And from the time of slavery, people with one black parent and one white parent have been identified by the larger society as black: first by law, then by custom. I know several black people who look white, but they just are not accepted as white or bi-racial in the white community so they self-identify as black where they are accepted and feel more comfortable.
not really... in this day and age, it's what is politically expedient and what will maximize one's wallet.