[This entry has been revised: I didn't read the MediaNet release carefully enough...they are offering DRM-less MP3s, not WMA files. Apologies to anybody whom I misled. My bad.]
Before this move, iTunes and the iPod were technically linked: if you bought a song from iTunes, you could only play it on an iPod (unless you burned it to CD then re-ripped it into an unprotected format). Offering DRM-less downloads severed this link, allowing users to play downloaded iTunes songs directly on a Zune player (one of the few portable players other than the iPod to support AAC), and making the MP3 conversion process easier. But by and large, the landscape didn't change much. The iPod already has 70 percent+ of the market, so there just isn't much demand for playing iTunes songs on other types of devices.
Today, MediaNet announced that it, too, has licensed more than 1 million DRM-free tracks from EMI. MediaNet, which just changed its name from MusicNet, is the back-end store for most of the second-tier music download stores (iTunes is the only tier-one store, with something like 80 percent market share), including Yahoo Music, MTV Urge (heavily promoted by Microsoft before it launched its own Zune player and store), and Samsung Digital Connect (Samsung's response to Zune).
Equally important, the DRM-less downloads on the MediaNet stores will be in the MP3 format. While AAC (and Windows Media Audio, for that matter) offers a much better quality-to-compression ratio, MP3 is supported by all portable players, all digital media software for all computer platforms, and far more consumer electronics devices than any other compressed digital format. This could actually change the landscape: paid downloads, from one of the major labels, playable on an iPod, from a source other than iTunes. That's new.
The challenge to iTunes' hegemony could accelerate when Amazon launches its MP3-based store later this year. If EMI and the other smaller labels offering DRM-less MP3s begin to see their digital sales rise, then the other big labels might follow suit. And once all tracks are available in DRM-less MP3 format, the only differentiator for the iTunes store is the fact that it's integrated with the iTunes software, which is required to use an iPod (or iPhone). That integration should be enough to keep iTunes in the lead, but now these other stores have a fighting chance to compete on pricing and selection.