South Africa's ruling alliance has always placed strong emphasis on the notion of "decent work", and some of the informal jobs - those beyond the reach of the tax inspector, unions, insurance etc - included in Adcorp's calculations presumably do not fall into that category.
Indeed, one of the foundational linguistic theories of the twentieth century, which came to be called the Sapir-Whorf hypothesis, was based in part on the work of Benjamin Whorf, an inspector for the Hartford Fire Insurance company.