I musta missed this, but looks like YouTube promotes the legal purchasing of music via iTunes and Amazon’s MP3 Store. When you watch a music video on YouTube, there’s a Download This Song bar showing the legal sources of purchase such as iTunes and Amazon. Even when the song is over, there’s a bar in the video leading viewers to buy the song.
That’s a good way to build up good karma, YouTube. Or maybe it’s a maneuver by record labels to try to recoup lost single sales?