The "casting couch" is not only in Hollywood. You have lots of attractive women competing to get the slot in front of the camera. It would not be surprising if a number of them decide that sleeping with the guy who makes the pick is the way to get there.
The percentage of people in front of the camera is small compared to the percentage behind the camera. Especially true when you factor in all forms of media, not just TV. This percentage is for the overall number and 41% that have admitted as much tells me that people who live in glass houses should not throw stones, particularly not at brick houses.