It's not that some folks choose to abuse the system or not. I reckon ADSL users fall into three categories:
1. Businesses using dsl for everything from basic connectivity to hosting their email server and corporate website(s), VOIP and VPN's and are just trying to operate an competitive internet connected business for the lowest possible expense.
2. Heavy technically oriented private users who download games, videos, music, use p2p apps, skype, play online, stream media, etc.
3. The affluent guy/gal/family who wants permanently online internet as it's the latest thing and who really only ever use it for email and browsing.
I really don't think there is a defined group of users out there who set out to "steal" as much bandwidth as possible as an end in itself. They're all just trying to accomplish something else primarily, and if they find a way of using more than 3GB, I doubt they give a damn about some technicality on Telkom's part about the quantity of electrons they can get through their modem in a month.