I don't really understand this phenomenon. You're posing for a photo with a girl, you reach an arm around her, and then don't physically touch her.
If you did follow through, even if the girl was uncomfortable with it, she probably wouldn't make much of a scene and would avoid ruining the photo over it. Alternatively, if you feel uncomfortable making said contact, there are plenty of respectable poses you can strike for the camera next to a girl that require little to no contact. Why in the hell would you attempt to create the illusion of the "arm around shoulder/waist" pose at the high risk of making yourself look like a massive faggot in a photo that others will see?
What's even more bizarre is when the woman IS making physical contact but the man is not. How are you so much of a bitch that you can't touch a girl who is already touching you?