Apparently the photo inspired this woman to save two men from an oncoming train:

The statistic advertised in the subway is that 150-some people are struck by trains annually and 40-some are killed. So whether the photographer could have saved the guy who fell in the tracks or not, if the photo raises awareness about the hazards of the subway and inspires people to be aware of their surroundings and to help people in danger, then maybe it does more good than harm.