Why? Why do they have to cut me off eventually? Throughput (which is what they're talking about here, not bandwidth) is essentially free. It doesn't matter if I download 1 GB, 10GB, or 500GB in a month. It is the bandwidth that costs money.
If I download, constantly, for 28 days, at 512kb/sec, I'll use 1209.6 gigabits of data. That's well over all of their caps, but 512 kbs is a very small amount of bandwidth and a very cheap line.
With their standard cable internet plan, at 6MB/sec, I can download for less than 14 minutes and hit the 5GB cap, 27 minutes for 10 GB, an hour for 20, and 2 hours for 40. That's not including their faster packages.