It's not so much relevance to real-life as it is having more nuance and sophistication than trite clichés and sophomoric humor. Adults look for more depth and multi-faceted qualities in order to be stimulated, not just ad nauseum repetition. At the same time, all this nuance and sophistication has to be packaged and paced to fit into the adult's schedule. While we may be willing to play a long game, one that will keep us occupied for weeks to months, the game cannot require singular 4+ hour sessions in order to make progress. At the same time, during that entire weeks to months play time, the game cannot use typical time-lengthening tricks, recycling of content, and repetition of action to give the illusion of a long game. Adults see right through that sort of stuff and become completely dissatisfied. Kids love repetition because their minds are built to learn by near endless repetition. However, the adult mind "gets it" after just 2-3 iterations and is ready to move on after that. Asking the adult to perform anymore repetitions than that, without setting up some meaningful purpose or goal where the adult can logically understand the need for the repetitions, will lead to tedium, boredom, and then abandonment.
Making a game for an adult requires more sophistication and refinement of the art. When I say art, here, I don't mean the fine visual details or obtuse abstracted scenery. I'm talking about the construction of the game itself. The pacing of the content, the fluidity and fit of the controls. I'm also talking about the themes, the dialog, the situations and issues, the character design. Literally everyone in and about the game has to work as a seamless whole that evokes its own unique identity. That is the art of games. It's the craftsmanship that is put into the holistic construction of the game.
Most of the games that have been served as examples of games as art are really just pretentious pretenders that fail to understand the true art of game design. Instead, they substitute gauche abstract visuals, nebulous stories, and reckless pacing as being artistic (when it's really all just a mess, much like most of the modern abstract art). They fail to understand that the art of the game exists on the holistic level in the totality of the game's construction and its interaction with the player, not in the individual details. Also, being obtuse and difficult to comprehend is not necessarily artistic, in any medium; it's usually more indicative that the "artist" really just had no clue what he was trying to do or how to do it.
Getting back to the main point, adults require games that stimulate on an intellectual and spiritual level (do not construe this as meaning the game has to be religious or have religious themes; though there is no restriction against such to achieve this end). They require games that get to the point of what they want to say and don't waste time mucking about in needless time-extension simply to give the illusion of copious content (an adult can easily see when a 60 hour games is really only 30 minutes of actual content with 59 hours and 30 minutes of filler and grind). Adults want games that are refined and sophisticated, not clichéd and childish. This is not to say adults don't like occasionally engaging that sort of stuff, but we become fatigued when that is the only thing available. Real-life relevance is not necessary for the adult to be engaged in a game (adults very much like fantasies, too), however, at the same time, there is no restriction to this. Don't make the mistake of thinking there is a single "magic-bullet" way of making a game that appeals to adults (in fact, this mistaken "magic-bullet" thinking is what is wrong with a lot of "solutions" to various issues, but that's a different rant).
