There was a brief time at the beginning when they used Fairplay DRM on audio because they were forced to, despite many pushes from them to get that dropped. I believe Amazon broke that one and was the first DRM-free store - not entirely sure on that one. iTunes store followed shortly after, as soon as the studios let them.
Apple do use DRM on their bought/rented video from the iTunes store. But then so does Amazon, and so does Netflix, and so does MS. They're in exactly the same situation.