The fact that they were leveraging their monopoly in digital players to advance a format that stifled competition is.
*Cough* Bullshit. At no point in time did Apple have a monopoly on digital players. In fact, one of the biggest competitors in this market is the Windows PC, which millions of people use and can play many open audio formats such as MP3 which people purchase from competitors such as Amazon or Rhapsody. 10 years ago there were plenty of competing digital players, which all ultimately failed in the marketplace following Apple's success with the iPod on their own merits or lack of consumer perception of merits compared to iPod.
It just turns out Apple had popularized many innovations in the digital player space, and it was not as if Apple added on DRM later to snuff out competition, they came to market with these features at time of the 2003 launch of the iTunes store. For example, in 2001 Apple launched the iPod. There were plenty of digital players at the time such as the Creative Labs Nomad Jukebox or the SonicBlue Rio.
Last I checked; antitrust legislation doesn't mean you're under an obligation to help competitors interoperate or consume components of your product.
Shoppers at the iTunes store willingly accepted this DRM, at a time when there were competing alternatives Such as Microsoft Windows Protected WMA and RealNetworks Helix used by other digital media playing devices.
The iPod connected via firewire; it synced with a PC using itunes, and it contained a hard drive with an innovative Anti-Skip feature; at a time when nearly all the digital players were using limited capacity flash, Microdrives, or required a burned CDROM to be inserted.