Analysis from The Economist -- see the full article for more speculation about possible reasons for the Apple move, timing, etc.
The music giants are trying DRM-free downloads. Lots of smaller labels already sell music that way. Having seen which way the wind is blowing, Mr Jobs now wants to be seen not as DRM’s defender, but as a consumer champion who helped in its downfall. Wouldn’t it lead to a surge in piracy? No, because most music is still sold unprotected on CDs, people wishing to steal music already can do so. Indeed, scrapping DRM would probably increase online-music sales by reducing confusion and incompatibility. With the leading online store, Apple would benefit most. Mr Jobs’s argument, in short, is transparently self-serving. It also happens to be right.