These plans fall short of the 250GB limit Comcast has imposed. To avoid irate customers, AT&T has claimed they will contact people who exceed 80%. That would definitely be important, as once they hit the cap a customer can be expected to pay $1 per gigabyte for additional bandwidth.
While all of these companies make similar claims – that a small percentage of users consume most of the bandwidth – most of them blatantly ignore the fact that the Internet as a medium is changing. In a few years, streaming video is likely to be the norm, rather than the exception.