^Not entirely true. There are a few sites where you can purchase movies and download them. CinemaNow is one such site. The price for the movie is not discounted very much (if at all) from the disk price, and the quality is questionable. If they keep it in mpeg2 and only offer 2000kbps average bitrate, then they will be rather poor quality. If they are offering H264, then the quality should be good. I don't use CinemaNow, so I don't have examples of their downloads.
Of course H264 video won't work on many regular dvd players. It might work for those that have mkv or mp4 support.
Blockbuster On Demand Movies also offers downloads for purchase as well as streaming video.