This study is definitely flawed. It costs approx. 10-15 INR (0.2 USD) for a milk coffee, not 1.51 USD. Even at Starbucks, it would cost at most 1 USD.

first off, you're calling bulgaria, india etc. poor countries. relatively, okay, but op was about even poorer countries. But more to the point the prices you quoted were about buying coffee in restaurants. Most people drink their coffee at home (or at work) not in shops. And it's much cheaper then. E.g. I usually drink senseo and it costs me about 25 eurocents per cup.

You might be surprised but if coffee is imported, it might actually be cheaper in Europe than in these poor countries. Import duties, corruption, bad port infrastructure... all of these issues inflate costs.