There is also a "cart and horse" issue here: Where is the pervasive content?
Most content providers don't want multicast because it breaks their billing model. They can't tell how many viewers they have at a given moment, what the average viewing time is, or any of the other things that unicast allows them to determine and more importantly bill their advertisers for. There is no Nielsen's Ratings for multicast so that advertisers could get a feel for how many eyeballs they are going to hit.
I worked for a startup in 1999 that was doing just that. Neilsen's for multicast. It was cool while I was there, but it quickly became clear that the product was ahead of it's time. They now do event streaming and I think they support unicast and multicast. Without a network that supports it, multicast apps are useless. jas