Why is Game of Thrones aimed at such a mature audience?

The books are just as graphic (and perhaps more so) than the show. Just keep reading. In fact, way before the TV show was a reality, the books' author had stated frequently that if his series was ever to be turned into a TV show that only HBO could do it, because they wouldn't cut out the whole lot of sex and violence that are in the books. True, there are a few extra sex scenes that are not shown explicitly in the books, but many more are definitely implied. The reason for this is the different narrative methods used by the two mediums.

In the books, the story unfolds in a POV (point of view) style where you see only what the chapter's character sees. As you mentioned, Bran sees the Lannister twins having sex but he interprets it as two naked people wrestling. Innocent and naive Sansa refers to her stomach with the childish word tummy. And so and so forth. So, there are many events that are never actually witnessed by the POV characters (and thus the reader) and are second hand reports (subject to unreliable narrator).

On the other hand, the TV show follows the action rather than the main characters, simply because that's a lot easier and more effective in a visual medium. Thus many events are explicitly shown rather than being second hand reports. This results in extra scenes (not just extra sex scenes). For instance, the scene where Tywin is chastising Jaime while skinning a stag is not in the first book, since neither Jaime nor Tywin have their own chapters in that book. But we do know from various reports that Tywin was unhappy with Jaime's actions, we have just never witnessed it first hand in the books, which is something the TV show can allow us to.

The reason that Game of Thrones is aimed at such a mature audience as either the book series or the TV series, is at least in part because the entire story is the complete opposite of the romanticised "knight in shining armour goes forth and does great and honourable deeds". The entire premise of the story is that of the reality of medieval life and war, which was at best, nasty, brutish, and short. On top of that the honourable knights of the Kingsguard are wearing tarnished armour, one is a sycophant, one is trying his best to stay out of the war, one is an oathbreaker and kingslayer, and the best of them all has been deemed "too old" to serve his post in spite of his dedication to service.

Then there are the other knights. Knights like Sandor and Gregor Clegane. One is a raging psychopath who feels no remorse for the suffering of other people, and actively enjoys causing that suffering. The other one just likes to kill and despises the title of knight for all the things his brother does. Knights lower than they tend to be barely better than brigands, and they all end up doing terrible things in the name of whatever lord they're serving at the moment, regardless of how good their intentions were.

The overriding lesson of Game of Thrones is that being the good guy isn't enough to win a war, that war does not determine who is right, only who is left, and that honour has nothing to do with it. The kind of moral ambiguity in the series is certainly above the understanding of children. Who's the Good Guy? Nobody is. All men must die. All men must serve. And don't piss off Walder Frey.

Plenty of sex and gore in the books. Whether the sex appears in the same place in the TV series as the books is pretty much irrelevant.

There's a problem with presentation though. Unless you're talking outright erotica, descriptions of sex rarely work well. There's a reason there's a "bad sex award" for books. So writers typically avoid long descriptions of it - suggestion is more effective. TV and film don't have the same problem.

As for "more mature", you're reading a series of books where people are regularly raped, tortured, burnt alive, and just generally killed. It's not your nice fluffy hobbitses. If there were ratings for books, the series would definitely rate 18 as well. Except perhaps in the US, where graphic violence is rated 15 but a single exposed nipple gets you an 18 rating. :/

In simple words, Sex adds to the whole feel of it. Take it or leave it, it does attract a lot of audience.

And yeah, since I have read the books, I agree that most of the (sex) scenes are exaggerated. But people like it and they watch it and so they spice it up wherever they can.

Another single word: HBO. HBO's target audience has always been more adult than broadcast TV. They even allow curse words and nudity that are illegal and would be a fine if shown on broadcast TV.

The Martin books depict a brutal, violent, ugly world, often in the throes of war.

It's not a Disney story, and since there is torture, rape, flaying skin off of victims and cutting off body parts for sport, any attempts to make it "PG" are going to ruin the story. Since we're already in adult territory, showing breasts doesn't make it any less kid-friendly.

This is more about some people's hangups about sexuality. There's a long history of people freaking out over seeing a body part, but being fine with seeing a skull spit open or entrails spilling out, when it comes to movies and shows. Adult is adult, and this show is adult, nudity and sex or not.

Many writers and directors said that they use sex scenes because that what viewers want to see. Examples of writers/directors are, creator of True Blood, Masters of Sex.

Game of Thrones (books) contains many sex scenes but the sex scenes in show are exaggerated. It's HBO show so it must contain sex scenes.

It's the same thing with Orange is the New Black. In the book it said that in the prison there wasn't any lesbian relationships. The show is all about lesbian sex.

I'm not against sex scenes in TV show, I even hate when we show actors with clothes making love. What I hate is gratuitous sex scenes. For Game of Thrones when I watch the show for the second time I watch the censored version.