Not quite accurate
Centurylink has a soft cap of 250GB for those with plans offering more than 1.5 Mbps, but there are no fees for overage. I guess they warn you and possibly disconnect you if you keep exceeding it?
They are trialing a new usage based billing scheme in Yakima, WA that presumably will eventually roll out everyone else that has a limit of 600 GB for those with plans offering more than 7 Mbps, and imposes fees for going over that.
At 3 GB/hr for the highest quality HD streams from Netflix, you'd need to stream 200 hours a month to hit that. Possible for a big family I'm sure, but since I don't stream all that much or run Bittorrent, I've never encountered even the 250 GB cap I'm currently under.