From Economist story that declares, "The democracy bug is fitfully catching on.
I would argue two observations: First, the impact of South Africa is crucial for the beachhead in the south; and America has had some role in enabling the weaker beachhead in the West.
Good underlying trend seen in second accompanying chart:
If the Chinese and Indians and Arab sovereign wealth funds now represent the dominant economic dynamic in the region, then you cannot say that it's resulted in more coups, even if the progress toward serious democracy is "fitful."