Originally Coraline was scheduled for September, even though it's been finished for quite some time, and I'd suggested to Harper that it might be fun to release it on Audio in May/June. Audio books tend to be seen as strange little unimportant parts of publishing, and I thought it would be interesting if the audio was very much and very obviously the first edition. It seemed like a good way of getting people to stop and listen to it who otherwise wouldn't -- and I love reading it out loud. I thought it might be good for a few interviews or articles or reviews, and I could talk about why audio books were important, and what the difference was between reading a book yourself and having it read to you and so on.
Then, at the last minute, a major retailer in the book trade whose identity I shall not reveal here, masking them instead behind the impenetrable nom-de-blogger of "Farnes and Groble" pointed out to Harper that they had a lot of things happening in September, but nothing at all in July, and they'd get even more behind Coraline if it came out in July.
And, in moments, Coraline had a July 1st release. The audio release is still earlier, but now it's about 20 days earlier rather than 5 months, which is not really enough time for anyone to notice.