Here was my reply:
My mother and I always laugh about "movie sex" (you know, the perfect lighting, the carefully arranged body parts, the slow motion, the smooth music, no sweat, no bruises or unexpected bodily noises). Let alone the emotions, where couples who are going to stay together always seem to have perfectly happy sex. You seldom see "I'm mad at myself and I'm not all that damn happy about you either" sex in movies, though it's not at all uncommon in reality.
Which is why I went more explicit with the characters in the scene I linked to above, since it was necessary to show how conflicted her feelings are (about a lot of things), and she mostly only expresses herself in sex (the rest of the time she's pretty careful what she presents to the world).
I was less explicit with the married couple here because what was interesting there was the conversation they had on the deck, not the sex itself. Which is another complaint I have about sex in movies. Conversation after sex is almost always mushy stuff, whereas in my experience post-coital conversation can range across any topic in the world (including, but certainly not limited to, the sex and the relationship). Which is why both couples at Perry's house cover quite a few different subjects in their "pillow talk."
I was less explicit with the younger lovers here, because of the reason above, but also because of a desire not to feed anybody's fantasies.