As an older gamer, I'd like to see my preferred form on entertainment, that is video games, have the freedom to touch on some of the more adult themes that are common place in the main stream movie industry. I'm not talking about porn games, though I don't have any problem with those either. Strickly pornograqphic titles, be they movies or video games, will almost alway be in the fringe market. I'm talking about, for instance, a video game with the same type of adult themes and content as the film Antichrist. That's a pretty graphic film in all respects. Right now we'd never see a mainstream game with that level of graphic depiction.
Ok, I'm starting to see where you're coming from. You're wondering if we'll ever see even more violence and even more sadistic behavior in video games. I think that's certainly possible although video game companies want to make games that will sell so they can make money. And the more violent and sadistic you get the less population of people will buy it. I looked up the movie you mentioned on Wikipedia and saw at the bottom that they are planning on developing a video game based on the movie in which the story would pick up after the events of the Antichrist movie. Whether or not we would ever see that game in stores remains to be seen. But at the same time would we ever see it through Impulse or Steam or Direct2Drive?
The point of your post seems to be that retail stores are prudes and so it doesn't matter if a developer makes an incredibly sadistic game because they might be able to retain their sales goals by being digital download only. My guess is, however, that (again) the more sadistic and nihilistic the game becomes the less appealing it is to a wide audience; even if it has some truly great gameplay. If the developer is dedicated to the game and doesn't care about how much he makes then he could definitely still make the game but he may only be able to sell it through his own website. Impulse, Steam and others may turn it down just like retail stores would.
Finally, your point about the USA being too conservative for this kind of thing isn't really valid. There are many, many, many more countries that have far stricter obscenity and censorship laws than the USA. Especially in video games.