If I understand you correctly, you're saying that women in an ongoing sexual relationship (married or unmarried) masturbate much more frequently than their unattached peers. Yeah, I can believe that -- the more orgasms they experience, the more orgasms they want, the little sluts! LOL
Apparently from society's upper crust, she learned at her exclusive finishing school that young ladies of her stature keep their breasts modestly covered at all times.
I'm not aware of the study you misquote. What we do know is this: Men who are sexually active masturbate less than their unattached peers. Women who are sexually active masturbate much more frequently than when they are unattached.
This was known even before Kinsey's report.