This sort of stuff makes me sad. But also strangely curious, since the suggestion is that these conditions are not survivable and yet people do survive. Are millions of people dying in Mumbai's slums and we're not hearing about it?
Its a very complicated issue.
Don't read too much into it. The fact that they live in slums has sometimes little correlation with their purchasing power or sometimes their financial status.
http://en.wikipedia.org/wiki/Dharavi
This slum is a mini industry in itself having exports of over $650 million an year. Its possible many people living their have their own cars or even their own homes else where, which they have rented out for some monthly income.