It's called "frumkite on shmootz". They think they're 'open minded' so they listen to classical music, they get magazines, they have medical books with naked women, the wife edits the magazines for the husband.....HAHAHA.
But when it comes to sex they're very frum. They hold that a husband and wife may never see each other undressed. It's a backwoods 'Kal Vechomer'. If the Torah says it's forbidden to have sex by the light (Because maybe you'll see something not nice on her body, and you'll hate her. Or because of Tznius) then even if you're not having sex you also have the same problem. But the problem is that the Torah never said that, the Torah only said "during sex". And you can make an argument that only during sex are you super sensitive, but not during sex you can see her body and play with her. OMG! Did you say 'play with her?'
You can also make an argument that the Tznius problem is only during actual sex, but just plain being undressed privately with your wife is not a Tznius problem just like a mikva is not a Tznius problem. And the proof is that even the Raayved who does not let you stare or 'go down' over there, never said that the problem was because of Tznius. And the 'Tur' who brings down the Raayved also says not to 'stare over there' "even though the husband says he will put out the light before having sex". So obviously the light is now 'on' even though she is naked.
I talked about all this in Feb 12, 2012. See also Nov 6, Dec 2, 2012, and Jul 31, 2011.