To swallow or not
I think when a women swallows your cum, firstly it does feel really good rather than spurting into fresh air. I think it is also a final act that means that the women will virtually do anything for her man.I suppose its like anal sex a lot of women just will not cop it but if they do sometimes it means again that they will do anything to please there man.
I think swallowing cum can be a power thing for a man. Quite often we are the ones that like to push the limits and see how far our women will go. For instance "hey babe if you really love me swallow my cum," ect ect.
Just my five cents worth.