There's a good explanation in http://www.dtc.umn.edu/~odlyzko/doc/net.neutrality.delusions... (2008) section 3 which explains "why faster-than-real-time progressive downloads of music or video are far preferable to real-time streaming. But first let us consider the strange situation in which this issue is not discussed publicly, and the advocates of each of the two types of video transmission mostly seem unaware there is a real alternative to their preferred solution, and that there is a serious decision that has to be made for each video service."