Bank interest will practically never exceed inflation. It's a guarenteed loos over time regardless of how it's compounded. The indi most likely will beat inflation by a fair margin.
Aside from that, growth in shares takes two forms, share price increases, and dividends. The dividends for the indi are paid every three months, but growth takes place at any time, and does compound just like interest. If you gain 2% this month, and 2% next month, the growth this month would be from say R60 per share to R61.20 a share, a gain of R1.20. Next month though, the same 2% would be from R61.20 to R62.42, a gain of R1.244.
If that keeps up, and it has for some time, you'll be faaaaaaar better off than some type of cash account earning you 6% p/a.
Here's your R1000 a month (increasing with inflation) in the bank at 6%:
http://www.investorchallenge.co.za/calc_compound.php?initial_deposit=0&monthly_deposit=1000&yield=6&years=20&inflation=6Balance of R749 516,77
And here the same R1000 a month (increasing with inflation) in shares at 15% (the indi has done 20% since inception):
http://www.investorchallenge.co.za/calc_compound.php?initial_deposit=0&monthly_deposit=1000&yield=15&years=20&inflation=6Balance of R1 894 004,61
So the difference is huge. Cash is not a good place to keep cash!
http://investorchallenge.co.za/the-only-way-to-get-rich/