Like most people here, I would love to cancel my cable TV and TiVo subscriptions and just get all my content on demand. However, aside from streaming every movie and TV show, Netflix/iTunes/whatever also needs to nail these two features:
1) Live events. Sports, breaking news, presidential inaugurations, etc.
2) Same day for new TV episodes. I don't want to find out what happened in The Office at the water cooler the next day.
The other hurdle is that the cable companies practically have a monopoly on broadband in many areas. I can already see how the call to Comcast will go.
"You're on the special TV+internet plan, which is $99/month."
"OK, I just want internet now, so cancel the TV portion."
"No problem, that brings your monthly bill to $98/month."
....