This theory came out at an interesting moment in how pornography changed, again in the 1970s. Previously, porn images with women in them tended to have the woman looking straight at the camera - an active participant in the taking of her picture, and in terms of looking back at the male admirer. If you look at early last century 'porn' images of vaudeville and burlesque stars, the woman are looking straight at you, via the camera. Very proud and straight forward.
In the 1970s, 'Playboy' began to take different sorts of photographs, of women who were pretending they were not being photographed. It was a true voyeur set up - where the camera was a man peeking at a women undressing etc, whilst she was oblivious to his presence. Views of her body were 'stolen' by the male, and there was a marked difference in how women in centrefolds were presented. They began to look away from the camera, look sideways, etc, and not present the bold one-on-one eyeline position. One now generally only finds direct eyeline matching in pornography where the women is being presented not as a sexual object, but as a sexually active dominant.
EDIT: May 13, 2012 And in an irony you couldn't make up, Blogger censored to of the images above. Here are the censored images: