Interesting survey. I disagree though that the finding is obvious.
We know that girls' hookups tend to be more attractive than their boyfriends - so its not obvious that they'd orgasm less with a hookup. Plus orgasms aren't everything for a woman. She'd still enjoy fucking say a male model even if she never came.
Alternately you could have said that sex in relationships is boring while sex in hookups is more dynamic and it would be plausible.
We know that girls' hookups tend to be more attractive than their boyfriends - so its not obvious that they'd orgasm less with a hookup. Plus orgasms aren't everything for a woman. She'd still enjoy fucking say a male model even if she never came.
Alternately you could have said that sex in relationships is boring while sex in hookups is more dynamic and it would be plausible.