believe it or not, jobs is pretty anti-drm, he fought against it for years with the record industries and eventually won. i read somewhere he tried to get the book publishers also to skip the drm, but they wouldn't agree to it. so they'll take a few years to learn their lesson and drop it as well.
apple isn't getting along with adobe right now, why on earth would they drop their own in-house developed DRM scheme to hand over a sack of cash to adobe to use their DRM scheme? makes no business sense, and i think their stockholders would agree, given that apple spent time and money to develop fairplay (that they tried to license out a bit years ago).
i think while apple is happy selling books, they realize it isn't going to be another cash cow like music and apps are.