When You Buy...
...a CD, you are purchasing a license to listen to, and play for your friends, the music contained on the media. If you are a professional, for example a Club DJ, the copy you rip to your hard drive has the metadata to allocate the performance rights money venues are already paying.
There are CD's and DVD's full of music that is licensed for unlimited uses such as scoring or sound loops for ACID music assembly.
For the labels, selling the license and a high quality download makes money faster than pressing millions of disks. Someone that wants to "own" a song will not object to the download cost for the extra bytes. Sony Software sells downloads, with an optional Disk.
On the other hand, sending a blue ray disk by post would provide a shorter start delay than downloading it on my 3Mb. One 10 G movie download would blow your bandwidth cap several times over. This will change, the 41 cent postage stamp will creep upward, and the price of Real Unlimited Internet will tumble. Netflix is ready at their end to stream very pretty content, but once the Physical Disk, and with it the Doctrine of First Sale are out of the channel, Netflix will find it harder to compete. Luckily, the Bean Counters at the studios will never let them stop pressing CDs, Blue Raze, Holodisk, or whatever.