If you go to South Africa believing that, you have a good chance of becoming one of the crime statistics.
Crime is worse in the townships, but there are a lot of hikackings and robberies in the affluent areas. And you can get killed for a mobile phone. Different cities have different dangers. The best way to know how safe an area is is to look at the houses. If they are surrounded by high walls with electric fencing and burglar bars - don't wander around after dark, be vigilant when driving. Also if you see a highjacking hotspot sign, do what it says and don't stop! These signs appear on the freeways so you can't avoid them if you are travelling between cities.
In general - J'oburg, Pretoria and Durban aren't safe. The Cape is.
Like anywhere, take advice from the locals - I've been about six times and have never had any problems. It's a great country to visit and the people are very hospitable. But there are a number of serious criminals - and they will see an influx of tourists as a feeding ground - just like the lions would in the Kruger!
The only crime I saw when I was in Africa was on Signal Hill in Cape town where a German tourist had had the straps to his bumbag slashed with a knife and stolen.
I would never dream of detering anyone from visiting what is a fantastic place but I`m not convinced the Cape is any safer than anywhere else.
Ok perhaps Joberg then.