The excellent free peer-reviewed net-journal First Monday has published an exhaustive survey of the earnings made by British and German musicians. Their conclusion? Copyright doesn't give creators a living, and in many cases (such as clearing samples) it costs them more than they can afford.
According to a GEMA (German collecting society) insider, only about 1,200 German composers can live from their creative output.
Only a small minority of artists reaches ordinary living standards from copyright income…
If an artist wants to include a sample from another record, major rights holders often insist on a controlling interest of 50 to 100 percent of the rights in the new track.
(Thanks, Rishab!)