Part of the problem is that with digital content, one doesn’t have the same rights as with print books and CDs. Customers own a license to use the digital files—but they don’t actually own them.
Apple (US:AAPL) and Amazon.com (US:AMZN) grant “nontransferable” rights to use content, so if you buy the complete works of the Beatles on iTunes, you cannot give the White Album to your son and Abbey Road to your daughter.
This is why I still buy CDs from time to time. Part of it is that I still prefer their sound (like how older people still swear by vinyl), but also that buying a CD equals tangible ownership of the music.