Yes, I think the index is more useful as an illustration of economic standard of living than its original PPP purpose. Although there is also the fact that McD's will gouge as much as they think they can from local consumers.

If a Big Mac is seen as an 'aspirational' good appealing more to the middle classes in a developing country as a sign they are successful and 'cosmopolitan', they can get away with far more than in countries where it's simply low-grade belly fuel, the street food equivalent of which probably costs far, far less per calorie in Kenya, Vietnam or Bolivia.

But it's also that 'aspirational' aspect which partly serves as a driver of hopeful economic migration.