Actually, most airlines change content monthly. VX has a pretty DEEP lineup of content, but I think the movies change on a monthly basis... but some of their audio content's been around for quite some time, for instance.
I'll tell you what... if AS manages to scrunch the DigEplayer 3.0 down to iPad size/weight (note: iPad has 10+ hour battery life), and includes Internet connectivity (browser/email) once GoGo wifi takes off, forget about seatback IFE. Why bother with the extra weight on the plane?