Several companies and content providers are actively working on Virtual MSO (Multiple Systems Operator), Intel, AT&T, and Sony to name a few. Some issues are startup costs, existing licensing agreements, and the fact that existing cable companies provide most of the broadband service in the U.S. I'm guessing, they wouldn't take kindly to competing services streaming content that was their exclusive domain?
By existing regulations, cable companies apparently couldn't block such content on their service? However, some have speculated that they could introduce metered bandwidth, which could effectively raise the costs for accessing premium streamed content to the point of making it not cost effective to the end consumer.