You believe the crime rate is higher? Or is it just that there's a semblance of a crime reporting system in place, where elsewhere, good luck.
It can be a combination of both. A large part of the South African population lives in the so called "informal townships" (comparable to the ghettos in the United States), where the crime rate is unbelievably high. Most of the other Sub Saharan African nations don't have these ghetto areas, and therefore the crime rate is somewhat lower.