There's a good piece by Saul Hansell over on The New York Times' "Bits" blog.
Hansell describes how Comcast is being criticized for low picture quality on certain broadcasts. That's interesting, especially in light of the contention between Comcast and DirecTV on this very issue, but it isn't the most important point in Hansell's post.
Hansell goes on to give a reasonable explanation of the basic issues involved, and mentions the likely future of cable TV: digital video distributed over Internet-like network switches. Instead of always sending every TV channel to every house, a switched system sends only the data for the channels that are being watched. (While it's fair to say that the capacity of such a system has no arbitrary limits, it isn't "infinite" as Hansell said.)
But there is a big practical difference between a system with hundreds of channels and one with, at least potentially, millions. With switched video, every channel is "on demand"--and anything that customers demand can be made available. Imagine YouTube in true HD, for example. That's impossible today, but with switched video, it's merely expensive. :-)
I wrote about switched-video technology back in 2001 in my column for Electronic Business magazine, and honestly I thought this technology would be in use by now, at least in test markets.
Verizon's Fios service has most of the necessary characteristics, but even Fios carries video in pretty much the same way copper-based cable systems do, except using an optical carrier over fiber. (Wikipedia has a decent explanation here.)
Well, there's no hurry. We'll get there eventually.