Going over 200 GB requires a lot of watching. I have a Roku box and a PS3 connected online, watch a lot of Netflix movies and MLB.TV games, and the most I’ve ever gone to in a month was 55 GB.
It’s not nearly as much as you think. HD streaming hits on average about 1.3gb an hour. Have a household like mine with 4 computers and two internet enabled blu-ray players that can simultaneously stream, and you can chew up 8gb an hour just with family members watching television.
Stream bandwidth varies. But let's say you want to watch an MPEG2 stream that is encoded for a DVD (5 GB, 2 hours.)
To exhaust 200 GB you need to watch 40 DVDs per month, or 80 hours. It comes down to only 2.6 hours of watching per day. Given that the TV allows you to watch news all day long (and generally to keep it on for no additional cost,) and also given that multiple persons in the household might watch their own selection of shows, the 200 GB limit is easy to encounter.
It's possible to play with codecs and reduce the bandwidth that each stream requires. Then you get a fuzzier picture, or you have to use more complicated codecs. It quickly becomes a science project. But people are used to watching TV as a free resource (except PPV, which very few people ever pay for.)