As daughters get older there need to be different boundaries. The same is true for mothers and sons. There is a difference between affection and what you described. I am speaking as a daughter, a mother, and a child and family therapist.
I agree with you 100%. I experienced an uncomfortable experience as a grown, married woman with my dad. It may have meant simply nothing to me at 19, or at 9, but at 27 it wasn’t right. It’s not as though my dad was being sexual, or anything like it, but it was most certainly inappropriate and uncomfortable to ME. The story being I have a terrible back, and I had just fixed a huge Thanksgiving dinner at dad’s for him and his girlfriend, as well as my sis and her family. I had my two kids, but my DH was deployed. I laid down on the floor saying “arghhh my back is killing me” and dad came over and gave me a good old back rub. Nothing sexual, again, or even sensual, and it was over clothes, also in front of everyone, but I felt really creepy about it. That’s the only way to describe it. I know I’ll always be his little girl, but in my mind I am DH’s girl, so dad’s affection was not appropriate.
Same goes with mother’s and son’s. We have a member of the family who is in his 60’s. For ten years he dated a lady (throughout his late forties and fifties) who had two children. He often confided how uncomfortable and creeped-out he was by the affection she gave to only her son. Both kids were adopted, and now I don’t know what that has to do with anything – but he mentions it, maybe trying to right it in his mind? So this mom does get overtly affectionate with her son often, and said family member says it wasn’t right, it was too sexual or sensual for mother/son contact. There was no cultural sensibilities to explain it away.

However, the son was not married, but then again well into his late teens early twenties – so who knows. I guess maybe more of the creep factor being she would be that affectionate to only the boy, and the girl she would barely acknowledge.
I think as children grow and change in many ways our acceptable affections shrink.