A-List artistes give out their music for free because currently there is no legitimate alternative. Currently there is no easy way for majority of 97m Nigerians who are actively connected to the internet via mobile to download music legitimately. But the music has to be heard and thats why the free blogs solve that problem for now. If MyMusic fills up that void, that will not happen again.
For upcoming artistes, they give out their music out for free because they want to get discovered and blow. This will continue to happen and that will become a major function of the blogs. Since they don't have access to the promotion methods that the big record labels have access to such as Radio, SoundCity/Hip TV etc.
BTW. artistes don't blow because they give out their music for free, save for a very few exceptions. They get discovered from Radio, TV, DJs, Clubs, Parties etc. and that's how they promote their music.