Both Cable and Web Video started out with a focus on:

1. UGC — the Cable Analogy I would use is Local Access — never before were people able to so “easily” have their content put on the airwaves. Granted, most of it was absolute crap, but interesting new formats often come out of young hellions on Local Access. Now, Youtube is local access—just on a much bigger scale. 
2. Syndicated Content — What really helped push Cable to become big was Syndicated Content from Broadcast TV and Films. People really did like re-watching episodes of I love Lucy and Seinfeld. Sure, not millions, and millions all the time, but there were some beloved shows. This idea has been exploded onto the web, with vast libraries being created online. In addition, syndication drove mainstream adoption on Cable—lookee here, Syndication drove mainstream adoption to the ONLINE video world.
3. Experimentation — While new creative formats such as Reality TV found their legs cable, I think it’s more important to think of the business models and added features Cable Created, such as Pay Per View, Video On Demand, Channel GUIDES built into the TV viewing experience. The interesting thing that Web Video really adds is the Fully Functional Search and Social Aspects
4. The Underdog Becomes Dominant through INTEGRATION — There was a time when it meant something when Jon Stewart made a gaff about being on “Basic Cable.” Can anyone say that anymore? Now, when anyone talks about Television they are including  a bevy of Cable Channels that are the real thought leaders. This is because Cable and Broadcast were ultimately integrated and became so ubiquitous—that there really was very little difference between broadcast and cable. With te advent of Google’s SmartTV initiative we’re on the precipice of seeing this happen with Web Video. Granted, it’ll still be 5-10 years, but at some point when people talk about watching a “favorite show,” there will be a second nature inclusion of Over The Top Web Video content.