Good question! The reasons can be varied and I'm not sure either. But where the charts were taken from, there are some notes on these countries.

Uruguay:

South America is pretty cheap across the board (especially in the Northwestern areas) but Uruguay is the world’s 30th most expensive country – hence the pink blotch halfway down the continent. However, you get what you pay for down there; Uruguay has some of South America’s highest levels of peace, press freedom, democracy and GDP growth. On another note, its population is also vastly outnumbered by cows; there are nearly 3.5 head of cattle per person.

Ghana:

Based on the countries we have the data for, you can see that Africa is easily the least expensive of all the world’s continents. The steepest prices can be found in Ghana, which is surprising considering South Africa’s huge popularity as a global tourist destination. Ghana ranks 38th in the world table, with the second highest being Mauritius at 49th.