I doubt they are pushing it back even though it's ready. May is the anniversary. It's likely being pushed back because it's not ready. Don't forget, Making of SW was already half-made since it is just a super-deluxe version of Charles Lippincott's aborted 1977 book--Making of ESB was an improvisation based on that book's success, and not only had to be readied in the same or less time, but it had to start from scratch, rather than just supplement an unpublished manuscript.

Sad, but in some ways understanable. Nothing official been reported yet, so who knows. I don't think there's anything malicious here though, book release dates often get moved around based on progress/editing updates, shame in this case as I was really looking forward to it--I'm sure the decision was based on the fact that releasing it early would result in an inferior product. Then we'd all be complaining about how crappy it is, that they are releasing something not ready instead of delaying it and fixing it (cough, 2004 DVD). I'm glad they are showing some backbone and commitment to quality in this decision.