People also want to know about the difference in general between US and UK book-covers. The simplest answer is, the publisher gets to choose the cover. What's appropriate for one country may not be considered right for another. There are fashions in book covers, just as there are fashions in everything else. And for Coraline, Bloomsbury have an overall look for the line of books they want Coraline to be a part of.
Just got an e-mail from Henry Selick, telling me the actress who was his first choice to play the Other Mother in the Coraline movie understands it, and has signed on. He sounds elated. And so am I. More news when I'm told I can tell.