In a marketing ploy best suited to a used car salesman, Comcast announced they would be offering over 800 channels of HD content by 2009. Of course, it's very easy to get that many channels when you count pay-per-view channels in an endless loop as a single channel. It also ignored Comcast's immense bandwidth constraints. Carrying 800 HD streams will consume 64Gbps of bandwidth even though a piece of coax can only carry a paltry 4Gbps. Their solution is to do what AT&T does and push the content to the node, streaming content on an as-needed basis to the consumer.
The big problem, however, is when too many people are watching at the same time. With hundred of subscribers per node and about 1Gbps reserved for data, voice and overhead, Comcast can realistically offer under 40 separate streams of uncompressed HD at a time. This means that Comcast will continue doing their infamous over-compression of television signals and offer HD that really isn't HD. Their HFC network is doomed to collapse under the strain of their over-zealous demands.
(See full article here.)