My wife visits McDonalds probably 2-3 times per week (so she's a "super heavy user"), always via drive-thru. She happens to be quite thin, she likes McDonald's for their coffee.
Just pointing out that statistics aren't always what they appear. About 99% of all money we spend at McDonald's is on (iced) coffee (which I'm sure is marked up heavily, but not as heavily as starbucks).
Also, the average calorie intake number is dubious at best. It's most likely based on a source (UN FAO) that cites it well higher than many other sources. The numbers I've found are closer to 2500 calories - probably quite a bit healthier than the Ethiopian numbers.