Just that I don't listen to many of bands/artists that put their songs on Amazon MP3 may make this offer less appealing.
I don't know much about this but cdbaby[1] will do that for what seems like an affordable price. It just takes a bit of effort and sacrificing some profits in lieu of better distribution. I'm not saying it's right for everyone, but it's possible to get music out there if you are an artist. And cdbaby will let artists choose where/how they digitally distribute so artists could just choose Amazon MP3 if they wished.