More coverage: Slashdot Techdirt
One small point: in the old days, format upgrades, say from tape to CD, often brought with them added benefits (better sound quality, more convenient access to songs, larger storage space, etc.) so there were actually justifiable reasons to upgrade. Now, switching from one DRM-encumbered format to the next offers no such incentives for the consumer.
I tend to think of it as ensuring repeated sales of their art throughout their lifetimes.
For a while there, ensuring this was as easy as making sure that your music was released on the format du jour. Records, 8-tracks, cassettes, CDs.... With the advent of digital music sans a physical medium, this trend of rebuying all of your albums is at risk. Suddenly, you're faced with customers never having to rebuy the White album, and you see your sustained profits going down the tubes.
DRM solves that. Now, rather than coming out with a new format every few years, you just have to come up with a new DRM scheme and turn off the old servers. Because the devices playing the music are somewhat general purpose, it's easy to move quickly--you don't have to worry about market penetration for the players, because it's just a free software update away.