The book, by the way, is Freehold by Michael Z. Williamson and is an excellent read if you like books about successful Libertarian societies with lots of military action and a moderate amount of sex. (I happen to like those kinds of books). You can buy it on Amazon as well as other places:
Well, in comments on the thread, some folk mentioned how they didn't like to read about explicit sex with the statement that "Sex is not a spectator sport."
Well, when I read, what happens on the page is not a "spectator sport" for me. I tend to identify with one or more of the characters and essentially live the story through them. My "identifier" is quite flexible and I'm fully capable of "being" for the course of the story, folk as diverse as Miss Marple, Herald Mage Vanyel, Kendra Pacelli, Bernie Rhodenbar, or Frodo. If you don't recognize all of them, that's okay. You can Google them if you want. Go ahead. I'll wait. Back? Okay, that said, when sex happens in a story I'm not watching it, I'm living it through the character. Let me hasten to clarify that I'm living it in my mind. This is purely an intellectual and emotional exercise. There's no physical involvement except my eyes moving down the page and my hands turning those pages. Okay? That clear? Good. ;)
So, when the sex in the story has no significant impact on the character development or story progression, that's one thing. George sleeps around a lot. He stops off at Jill's and, some time later, leaves while zipping up his pants. The sex is part of George's character but the sex act doesn't affect his character or move the plot. In this case, little more is called for than the bare fact that George and Jill had sex.
In other stories, however, the act of sex does have a significant effect on character development or plot. In those cases, I believe the sex does need to be "on screen" and told in exactly the same detail that any other plot mover/character development scene would be told. Sex with Jill didn't mean anything to George but with Ellen? Wow. There was something different about that, something that made all others pale into insignificance. Maybe it was because Ellen was the only one who really knew George, who knew the secrets George kept hidden from the world, understood him in a way that no one else can. That scene needs to be shown because that scene marks a change in George's character and to not show it is to give the reader no more reason for George's change than "because the author said so" (which rarely works). And when writers elide over those kinds of scenes (as was the case in many romance novels of a few decades ago--yes, this isn't the first time I've researched the genre) I find it jarring. It tends to throw me out of the story and I have to spend some effort getting back in.
Writers have no problem writing grisly murders, horrible tortures, and many other things when they are important to the development of the story and its characters (and even when they are not, but more on that another day). But a lot of writers and, apparently, a lot of readers (which gives an excuse for the writers) seem to shy away from presenting this one aspect in the same detail that these other things are shown. To some extent that has changed--particularly in the Romance genre if the paranormal romances I have been reading are any indication--but the stigma about explicit depictions of sex still seems to be there in a lot of fiction.
Not every story needs to have sex just like not every story needs to have a murder or not every story needs to have someone lose their job or not every story needs to have Timmy fall down a well, but it is, or should be, just as valid in a story as any of those other aspects. And if it is there, I believe the writer should be able to show it on the same footing as any other plot/character motivator. If the murder matters to the story, you describe it in detail. If the sex matters to the story, that, too should be described in detail.
Stories are about people. People, among other things, have sex. Sex is one of the more powerful motivators in life. That large numbers of people think that such a powerful motivational factor needs to be avoided or hidden in fiction has always struck me as odd. And while the taboos are breaking down, they are still there. And while they are there, I guess, writers will have to deal with that reality one way or another.