I started reading the books in 1997, and have watched every episode of the show. I'm far from a prude, but I've never been into porn - written or visual. I actively dislike it. Seeing other dudes naked is not my thing, even if there are naked women as well.
Point is...I've watched that show despite the sex scenes, not because of them. The writer's assumption that everyone else likes porn, and that's why they watch the show, is simply ridiculous. As is almost every other statement about what "everyone else" thinks or enjoys.
I do agree that most of the nudity/sex scenes are gratuitous and exploitative and weren't needed to further the story. I think HBO execs were afraid that if there wasn't nudity, they'd lose an audience that expects HBO to show nudity, whether gratuitous or not, because HBO always has.