According to this post over at BusinessWeek, Netflix accounts for 30% of the busy hour Internet traffic in the US these days. Combine this number with the 36 million subscribers they have and it's not hard to imagine that the Internet has the capability to evolve to support unicast streaming to everyone thus making broadcasting (i.e. multicasting a single stream to many devices) in the traditional sense obsolete.
It was not too long ago when I wondered if web radio streaming on a massive scale is feasible. Now 36 million households in the US stream video content over the Internet. That makes audio streaming on a super large scale seem to be almost a trivial problem.
Also from a network transport price point of view, audio streaming should cost almost nothing if you compare it to Netflix. For $7.99 a month you get an all you can stream video service. And the price does not only include the data volume transferred (on the Netflix side) but also the cost of running the servers and, not to be underestimated, the licensing fees for the video content itself.
The BusinessWeek article is quite long but contains a lot of interesting technical details. Like the 3 petabytes of storage in the Amazon cloud they require for their video content.