Mark Cuban discusses the various challenges. Among them: Bandwidth.
DVd quality at 1mbs is fine today, but have you noticed you cant do live consistently for any size audience at even this minimum bandwidth level ?
If someday the internet can support live delivery of 1mbs unicast streams, the cost will be prohibitive (every live stream requires a direct stream from source to end viewer), It adds up very fast. 1 stream per person. X number of streams per server. All the routing and internal backbone equipment to get it on the net. All the monitoring equipment to make sure it gets to the viewer in some semblance of decent quality. All the people to make sure that all works. Thats big bandwidth and overhead and hosting costs. Which is why 350k simultaneous streams at 300k quality for march madness and a concert were considered huge events in 2006. Every single incremental user for a 300k stream of a 2 hour event can cost more than $1 PER USER. (Dont think so ? call a broadband video provider and ask them how much they will charge to stream a live 300k stream to 350k simultaneous viewers with TV level quality of service).