We trade on Std Bank's live trading platform and those bids and offers do not even appear there. No doubt if I placed an order for R270m of shares it would spike the price 10-fold. So much for a level playing field in this rigged game!
My guess is that large trades are pre-arranged so that it doesn't shift the price. An investment house or two might shift stock between them and don't want or need to put it on the market because they've already figured out the buyer/seller. That's fine with me.