The Oberyn stuff is one thing, the Jaime/Cersei scene is another.
ASOIAF has a lot of world-building and regularly introduces characters whose backstories are really important. You're going to get either flashbacks or big chunks of expository dialogue. They've decided to go with the second (which is cheaper and more true to the source material), but every screenwriter has it hammered into their heads to not let characters stand around talking without anything visually interesting happening. So they're going to throw in tits or swordfights or even more tits. Sexposition's a cheesy trick but it's an understandable feature of the medium and the kind of story they have to tell, and ASOIAF's enjoyable in large part for the cheap thrills anyway.
That whole rape scene, though. That's making a really big change to one of the characters that actually gets some complexity and development, and who should be one of the more sympathetic characters in the show going forward. I read the books so long ago that I don't spot most of the changes, but that was jarring even to me.
PS Davos is the Hank Hill of Storm's End.
