While I agree our pricing should be lower with the stronger Rand, it's worthwhile pointing out two things:
1) The US pricing does not include tax, so you need to add 14% VAT onto the pricing for better comparison
2) Local retail pricing has an affect on pricing too, because if the game is released locally, then the publisher will likely set the price at the same level that the local distributor has worked out for the physical copies, which is generally higher than what it should be digitally. Yes, digital should be cheaper, but that's the way it is currently when there's a physical release.
So when you take into account the volatility of the Rand plus VAT and local physical copy pricing, the pricing isn't that far off. Of course some games don't get a local release, and then it's probably just based on a generic formula applied to our currency (some high FX average) + VAT. Hopefully we'll see pricing improve over the next few months, assuming the Rand can keep its strength up.