In regard to the various ratings around the world, how it rates is purely based on what 'someone' who assesses it thinks as to how it fits on the censorship rating. Internationally, there is a real issue with imbalanced ratings laws in relation to video games, and at least where I come from we have seen releases, then had them withdrawn for sale because the government is not bound by the 'guidelines' of its own assessment body...and that's because 'video' of the digital variety, or computer programs, don't fit into the existing limitations of the media laws, which only deal in paper, video tape, and other older established entertainment or other media.
Sorry

Rant over...
Skyrim is pretty close to paving the way in conceptualised advlt video gaming...it deals with some pretty lurid human emotions, although it covers it in a narrative well...but it truly is sick subject matter. Just think of how some of the scenes you have seen or come across would make a sicko doco or cop show.,,but the game is available very broadly. In regard to the decapitations, it's a bit more realistic than F3's splatter show, but it still isn't shocking. It's muted, and I personally would prefer longer cut-scenes of my kills, and a bit more mature a storyline.
If Beth are prepared to push the envelope, they are quite able to introduce a truly narrative advlt focused game in the future...and that will be the biggest marketting ploy since going on Steam (at least for PC's...Consoles are still seen as young gamers gear).