multicast video only works if everyone wants to watch the same thing at the same time.
most people who could use IP TV are not going to be doing this. They will watch the show they want to watch at the time they want to watch it, and the number of other people who start watching the same show at the same time is so small as to be meaningless.
For broadcasts of live events (political speeches, Sports events, etc) there may be a small niche, but is that really worth the effort of implementing it across such a large infrastructure?
remember that if people aren't consuming the content, all you are doing is wasting available bandwidth.