A couple of points.
a) you get MP3s, not CD quality.
b)You don't get booklets or notes
c)(Maybe Jean Ritchie can help me here) I don't know if artists get royalties; it certainly cuts into the artists' CD sales.

Having said this, I'm delighted to see that the music is now more readily available. I'm just not sure that this is the way to go for material that's already been remastered and put on CD.