The real world of data is generally billed at the 95th percentile of traffic consumption, usually with a commit to buy a certain amount of traffic. So you pay for a specific rate of data, the vendor provisions equipment to handle the agreed upon rate, and then you can do traffic at that rate forever. If you go over your rate, you talk to your vendor.
I don't know of any equipment whose natural operation is to handle a certain amount of traffic, then shut down until the next billing cycle comes around. Data caps are a measure invented to extract money, not serve customers or packets.
If the cable companies were worried about fairness, they'd really be speaking in terms of bandwidth reservations at peak times and encouraging use during off-peak hours, and similar things. They're not, it's just a money grab.