Not surprising free > paid. Since the apps are free and the music is not this makes sense.
Personally I buy my music in wholesale lots of CD's and Record's. The CD's for ripping to lossless for my iPhone the Record's for playing at home. It's still a lot cheaper than paying $1 a track on iTunes and better quality.
Purchasing music is very different from downloading apps (often free) apps. I would not really say that they are comparable activities, and the disparity between them doesn't have much relevance so comparing music purchases to app downloads is pretty meaningless.
The only personal media device I had before I began using smartphones was an ipod touch. At that time, I only used iTunes for digital music downloading. But (as the article mentioned), as options have advanced, and as I began using smartphones (android), I mostly abandoned iTunes all together. I mostly use Amazon mp3 for my music purchases (because amazon had mp3 downloads sooner than google play music did).