The workforce for the dhabbawallas is cheap and they live on a fairly low income. The way I understand it only a certain caste are dhabbawallas (correct me if I'm wrong).
Even though the number of deliveries is huge, the people being delivered earn considerably more than the dhabbawallas, they all have office jobs.
Having lived and experienced the Indian mechanism of things I am always impressed when this story resurfaces, but unfortunately knowing India I am very skeptical. They no doubt excel at what they do, but I would take the statistics with a grain of salt.
Ask yourself how it is possible to measure such performance?
The entire mechanism is so informal and excludes any 'reporting' (in the sense of data about efficiency) and is focused purely on delivery. I know a lot of "certified" companies in India that lack basic factory security, hygiene and protocols: they would fail a "real" certification.