You are completely missing the point of both my post and the OP. It's not about getting the best possible returns. It's about convincing non-savers that it's worth saving. Overcomplicating things with inflation and tax calculations is not going to help. Besides, even at 10% pa, it will take 3-4 years to exceed the tax-free alloance on interest (R23k odd) - enough time for someone to get a feel for the growth and realise it's worth it, even with modest savings every month.
You and the op are not painting a picture of "it's worth saving", you are both painting a "get rich" picture: "Become a millionaire, it's easier than you think", and "the bank is throwing money at you". This is an outright lie. All that saving allows you to do is retain wealth - by definition.
And speaking of which, I've moddelled those factors, with the SA figures. You still come out ahead of inflation ...
You don't, what you consider "ahead" is currency risk.
... and most definitely ahead of not saving at all.
Does this really even need to be said?