My DC One Million Omnibus turned up today! Glad to finally have it. I usually don't like pre-2000 comics (I was born in 1991, I don't know any better ), but this looks to be a fun story. And I don't think I've developed the ability to say 'no' to a Grant Morrison book yet.
DC seems to just release whatever they like, whenever they like. The only time I can remember them exploiting a movie release was with the Golden Age Superman Omnibus for Man of Steel.