Funnily enough ... as various sex scenes in this game allready showed us, this is not true.
Sex positions can add a lot to show a dynamic (top/bottom, or dom/sub). I believe there were complains about us being unable to choose.
It's narratively meaningful to some people. It's not to others. Whether a sex position changes how pornographic it is is another matter. I hope we can all agree that it /can/ be a tool to tell a narrative. Successfully or unsuccessfully. In some mediums, but not others. What would Fifty Shades Of Gray be about if not misguided BDSM
