Mark Suster is an investor in new net-based TV startups and in this 10 minute talk he breaks down ten reasons why Internet TV is ready to disrupt the industry. His full list of points and explanations is available on his blog, and in a presentation format.
It's a great bunch of ideas that take note of the weird transition period we are currently in. When I was giving away my old TiVo, I had trouble finding any close friends with a HD cable package that could even use the device. Almost everyone I know is either cutting cable completely for internet video, or cutting way back on their cable plans to the absolute bare minimums. My friends tend to be technology canaries in the coal mine, but the writing is on the wall, and in the next few years we'll definitely see a mainstream switch to online video (and cancelations of cable TV plans).