Indy Music, Meet iTunes Music Service...
CDBaby has inked a deal with Apple and Listen.com to do digital music distribution. The terms for musicians seem quite amazing. You keep all rights to your music. You get 91% of the profit, with only a $40 startup fee. You get paid a week after CDBaby gets paid. It seems too good to be true. What's the catch? Where is the downside?

So there's this bit of fine print:
"to give us legal permission to distribute your music, you must own or control the copyright for the sound recordings and musical compositions"
I have only a minimal understanding of the music industry, but I'm pretty certain that most artists are signed to an agreement that transfers the rights of the song and/or their particular performance of the song to the record label. So while this is a terrific way for artists who are just starting out to sell their music, it's not available to anyone signed to a big 5 subsidiary.
But I Am Not A Lawyer ™, and you're probably surrounded by several people who can provide more accurate advice than I can :).