The only part of this graph that goes to the point of the poster is the decline in paid digital downloads.
Actually, the paid digital downloads are increasing (red portion getting fatter, though sales looked sorta flat from around 2007-2008, they do appear to have always increased.) It's possibly the decline in CD sales that you're seeing.
BTW, good point about gross revenue not telling the whole story.
Oh, and it sure would be nice to see what happened from 2009-2011. I'm guessing digital continued to increase, modestly, during the
recession. FWIW, you can see how badly the recession hit them in the late 70's and early 80's.