Cable TV/Internet companies make money by selling premium services. That is, they make profit from selling premium channel packages, on-demand services, and pay-cable channels. As internet video option continue to increase, including an increase in legal online video sources, more and more cable TV customers are cutting back on premium cable offerings. This will ulitmately force cable companies out of the premium business.
How are they fighting back? By trying to impose capacity caps (e.g., 40 GB / month limits). This should not be allowed. It is really anti-competitive in that it is a transparent attempt by the cable TV companies to protect their lucrative cable revenues in areas where there is not real competition from other ISPs.
Saul Hansell in the NYT notes that cable companies are scared and are now proposing to hook up with the actual content producers to allow cable companies to share in revenues for downloaded content. Needless to say, content producers are have grave doubts about the approach. More info focused on Time Warner Cable from GigaOm.