Most importantly, these books consistently indulge in the kind of endings that teenagers want to see, but which adult readers ought to reject as far too simple. YA endings are uniformly satisfying, whether that satisfaction comes through weeping or cheering. These endings are emblematic of the fact that the emotional and moral ambiguity of adult fiction—of the real world—is nowhere in evidence in YA fiction. These endings are for readers who prefer things to be wrapped up neatly, our heroes married or dead or happily grasping hands, looking to the future. But wanting endings like this is no more ambitious than only wanting to read books with “likable” protagonists. Fellow grown-ups, at the risk of sounding snobbish and joyless and old, we are better than this.A lot of YA and children's fiction end on an "up" note. There's at least a thread of hope, or hopefulness, injected into the conclusion of even the grimmer YA novels (Peter Cameron's fantastically good Someday This Pain Will Be Useful To You) may be the best example. On the other hand, novels like Mockingjay inject a grim note into an *apparently* hopeful ending.
One could argue that, if you consider that most YA fiction is either narrated or focalized by an adolescent, the hopeful ending is the most realistic: at age 16 or 14 or 19, most of us do believe that things will get better, than upward progress is the really the only progress or trajectory our lives can take. Lack of experience is one thing that makes this perspective possible, and Graham's reaction to the "up" ending as unsophisticated and stupid makes the old mistake - one I am increasingly annoyed with - of confusing "lack of experience" with "stupidity."
But the real point I want to make is this: a great deal of adult fiction has an up ending. Almost every piece of popular fiction - film, book, tv - ends on an up note. Even the classics, which Graham seems to regard positively, do this. Jane Austen? Courtship novels end with a wedding. They end with happy couples about to embark on their lives together. Shakespeare? Well, the tragedies and histories don't exactly leave us chortling with delight, but the comedies? End with weddings. Happiness. Looking forward to the future.
How about Charles Dickens, my own beloved? Has Ruth Graham ever read any Dickens? Our Mutual Friend, or Bleak House, or The Old Curiosity Shop? Nicholas Nickleby? The impossible coincidences, inheritances, legacies, couplings, weddings - even when they recall sorrow (Little Nell's death) it's through a haze of happiness (Kit and Barbara's pairing, Dick Swiveller and his Marchioness).
Crime and Punishment has an up ending, for heaven's sake. So does Robinson Crusoe and Paradise Lost and The Adventures of Huckleberry Finn and Wordsworth's Intimations Ode and Jane Eyre. I think you could make a case that The Great Gatsby has an up ending. Haruki Murakami's The Wind-up Bird Chronicle, undoubtedly a complex and sophisticated novel, has an up ending.
Of course there are classics that don't end happily, with all loose ends tied up. Henry James is quite the purveyor of these - Portrait of a Lady, for example. Wuthering Heights, with all those miserable vile characters.
But the stories that are popular - they don't end in wrack and ruin, for the most part. I know this because I actually really like stories that end bleakly. A friend once said "It's a good movie if, at the end, you kind of feel like you want to die." And yes! This is true! One of the greatest movies I know, and also one with the bleakest ending I can think of, is the Russian film The Thief. It is a tremendous film, and ends terribly. It's great.
But who has seen The Thief? Much more likely that you've seen Love, Actually, or There's Something About Mary, or Star Wars. And the books, the fiction, that people read: most of it has satisfying, unambiguous conclusions. The couple get together/get married/reaffirm their relationship. The criminal is caught. Justice is delivered. The world is saved. Even in stories where there's something sad/difficult/devastating - say, maybe, Armageddon, there's an up ending - because the Youth will Go Forward Into a Bright Future.
Pretending that "adult" literature is sophisticated and complex and challenges triteness at every turn is absolutely dishonest in every sense of the word. The only way you could really believe this is to never have read any books at all. "Snobbish" doesn't come close to beginning to describe what's going on, if you're trying to stake a claim for the sophistication of the endings of adult fiction as opposed to that for younger readers.