I'm on Vodacom, no charge for DLRs but I would still pay for it. My issue is that when I SMS I know its going to a single designated device (very slim chance to a dual SIM), but with an app like WhatsApp, I've got no idea. An IM read receipt is not a confirmation in a business environment when there is a dispute where a DLR I can at least say we did or did not get an ack from your phone.
Keep in mind that with a smart app you can have it running on many devices simultaneously and any user could acknowledge it.
WhatsApp has it uses, but its not the SMS killer.