MTN is 2GB @ R149 (
http://www.mtnsp.co.za/shop/MTNDirect/Pages/DataDeals.aspx)
Vodacom is 2GB @ R149 (
http://www.vodacom.co.za/personal/phonesandpackages/deals?dealId=988)
CellC is 2GB @ R119 (according to article)
So technically the difference between CellC's new specials and the other larger operators' specials are only R30 if you compare directly, and R50 if you compare not from a pure value side, but from a recurring consumer's perspective. But then again, on pure value you also have the extra 2GB you can utilise from Vodacom for things like automatic updates using Nightowl which would put them ahead of the other specials.
Anycase, well done CellC - pricing looks good for the consumer.