So I recently figured out that people want the same thing from advertising as they do from fiction: an emotional experience. In advertising, that experience is designed to spur you to buy, or at least think favorably, about a product or service--which may or may not be an admirable goal. In fiction, that experience leads to ... what, exactly? If there's a purpose beyond giving the reader pleasure (and I don't think there needs to be), perhaps it's strengthening the reader's capacity for empathy. Some studies show fiction actually does do this, although it could still be a chicken-and-egg problem (maybe more empathic people tend to read more in the first place).
At any rate, at the heart of both successful fiction and successful advertising is people's hunger for emotional experience. Not just pure experience, though--it somehow needs to be at a remove, so that it's safe and understandable, as well as powerful. You want the experience plus the meaning, or the solution. Fulfill that hunger, and you've got yourself a happy reader, or a willing buyer.
All of this reminds me of a scene from the first season of Mad Men, which has always stuck with me. Here, Don Draper presents his campaign for the Kodak slide "wheel," which he has renamed the Carousel. I find this a tremendously moving, and telling, scene. It's layered by Don's own nostalgia for a childhood he never really had, and for a family that, even now, is not exactly his (because he cheats on his wife, and, as we begin discovering in this season, he's assumed another man's identity). His longing exists, as perhaps it does for all of us, because he can never have what he seeks: a true home, an ideal past. He can only have a substitute, or talisman--the slides, and the projector that lets him see them. But the scene is also powerful because it illustrates the genuine power of advertising. There may be something sinister or shallow in its motives--the bottom line is always shareholder value, and eventually the projector will end up in landfill, or, as in my family's case, in a box in the garage marked "SLIDE PROGECTOR." Yet the emotion the campaign generates, in Don and in us, is anything but false. And that's why we still, at least somewhat willingly, respond to ads and to fiction: we want this genuine experience, in any form we can get it.