How Much Do Musicians Earn From Digital Sales?

How much do musicians earn from digital sales? SOPA co-sponsor Representative Bob Goodlatte (R-VA): "Intellectual property is one of America's chief job creators and competitive advantages in the global marketplace, yet American inventors, authors, and entrepreneurs have been forced to stand by and watch as their works are stolen by foreign infringers beyond the reach of current U.S. laws. This legislation will update the laws to ensure that the economic incentives our Framers enshrined in the Constitution over 220 years ago—to encourage new writings, research, products and services— remain effective in the 21st Century's global marketplace, which will create more American jobs." The main proponent of SOPA is the RIAA (Recording Industry Association of America). However, we still do not see musicians standing up and fighting fervently for SOPA. Why? Let's look at how much musicians actually earn through digital sales: <http://www.informationisbeautiful.net/2010/how-much-do-music-artists-earn-online/>