I don't know how accurate the number on the VG site are, but they say between RS and RS 2014 about 3.41 million units have been sold. http://www.vgchartz.com/gamedb/?name=rocksmith
picked up a copy for $18 and have played with it a little bit. Its better tan I thought it would be and I like the Hendrix tunes, but I'm disappointed that there won't be future DLC. I hope someone buys the assets with intention of providing support and releasing more DLC. Never hurts to have competition.