I half expected it to slide off too, there are no constrained groups in there. I guess what you can't see is that the hole isn't as large in the neck as it appears. There is a transmap in there to create the lace around the neckline. Maybe that's what kept it from falling off her shoulders, I don't know. Probably a combination of that and the pose kept it in place.
I won't remodel to make it a unisex thing. I made this a long time ago for Sydney. I just scaled it to fit her and ran the simulation.

If I had a nickle for ever time a woman told me to get lost, I could buy Manhattan.