Gaiman went up to his office and started trying to write it. “I read the first page,” he laughs gently, “and I thought, ‘This is a better idea than I am a writer. So I will put the idea away until I’m a better writer.’”The weird thing (at least to me) is that they keep referring to it as YA in the article. To be honest, I didn't see The Graveyard Book as YA. Would teens enjoy it? Yeah, sure, especially if they're already Gaiman fans.
But I saw it as a middle-grade novel--admittedly one with a rather more traumatic beginning than you usually see, but this is the same group we make read Where the Red Fern Grows, so I don't exactly see the objection. Gaiman himself admits that he has 10-year-olds reading it. So wherefore the YA? Possibly it gets slightly more respect than "children's book." Who knows.