Why not?
I recently saw the film Summer Clouds, which was about Robert and his cousin Marta playing a game with holidaying couple Daniel and Ana, attempting to seduce them, with the game being won once either one had sex with the husband or wife. The films shows us that Daniel and Ana are a fairly typical couple and are happy together. While Marta can't go through with seducing Daniel, Robert successfully seduces Ana, and while she is in a room changing, Robert enters, closes the door behind him and begins kissing her. The shot then changes to a shot of the door from outside the room, and it sits there for a minute or two. No one leaves the room, so the audience knows that something is happening between them but never finds out what exactly. Daniel suspects his wife cheated on him, but she denies it. Marta reveals the game to Ana, and tells her that nothing happened between her and Daniel, and asks if anything happened between Robert and Ana, but Ana refuses to answer. Robert tells Daniel it doesn't matter what happened as his wife loves him and they'll now leave and return home to their lives. Besides, Robert got what he wanted and was no longer interested in Ana. In this film, it was important that we don't see the sex scene, leaving us in the same position as Daniel, not knowing exactly what happened.
In the film Unfaithful, married Connie begins an affair with Paul. She is happily married to Ed, and the film shows the audience that there isn't a problem such as a lackluster sex life that leads to the affair. Her interactions with her husband are nice and sweet, while her interactions with Paul are passionate and intense. In this film it's important to show the sex scenes between Connie and Paul in order for the audience to see just how consumed by the affair and her lover she becomes.
I never said anything about cutting existing scenes out of movies, so I don't know why you are asking me this.
My point is that you can tell a story about sex without needing to show any actual sex. You can have no sex, like in Summer Clouds, or quite a bit of sex, like in Unfaithful. Or you can have a story where is doesn't even matter whether we see the act or not.
TV shows like Law & Order rarely show the actual murders taking place, because they are about finding the criminal and bringing them to justice. When a story is told from the point of view of the investigators, it's common for the story to start after the crime has taken place. And just to be clear I'm pointing out that tv shows and movies can be about crime and murder without actually showing the audience the act, not saying that it's fine to cut existing scenes out.
A war movie might be more concerned with how soldiers deal with returning home then any actual battles. Or a journalist in a war zone trying to cope the the violence occurring around them. You can make a movie about violence without showing the actual violence, only the effects of it.
I don't know of any other than Sims clone Singles, which is supposedly more focused on the actual sex but I haven't played it. Sex is typically something you'd see in a cutscene, whereas sex as a gameplay element is typically the stuff of porn games. In Mass Effect, it's basically just the payoff for completing the romance, and doesn't really add anything to the story. In GTA IV, Niko can go on dates with a number of women, and if they like him enough, he can have sex with them, although we never see the act. The point of these dates storywise, as with the outings you can go on with male friends, is really the conversations with the characters.