Sorry I haven't been here....had family responsibilities to attend to and haven't had much time of late!
Yes, the POTY thing will last as long as there is N supply to be had. Worse yet, our children gravitate toward the N parent and help give them that supply. It doesn't make sense to us but here's what I have come to see....
Our children know that we will always be there for them and that we will supply the unconditional love that they need. However, the N parent cannot and will not do that just by nature of what they are. Problem is, our children need that from both parents if at all possible and the N will dangle the carrot and give just enough to keep the child around and interested so that they can get their N supply. From what I hear from others with grown children, it doesn't always stop when the children turn 18, 21, 26 or whatever. The N will continue to go after the N supply and will do whatever is necessary to get it and it doesn't matter how or where.
The POTY act works even after the children are of age if the child hasn't ever figured out that the N parent is just using them. That can happen if the N parent gets custody/primary residence and then uses the time with the children to denigrate the "good parent" and turn the child against that parent. It can also work if the "good parent" doesn't stand up to the N parent and doesn't share facts with the child when necessary/appropriate.
With my boys, I make sure that they are guided toward figuring out when their father is using them for N supply. I don't tell them straight out. I don't knock their dad either. I give them facts and let them figure it out. We have joint/joint physical/legal and my ex got primary residence because I worked and he didn't (makes sense right?

) and I work hard to make sure that the boys aren't completely sucked in by N dad. Right now, N dad is trying to push the boys toward careers that will not only allow him to continue thinking he's FOTY and showing the world he is FOTY, but that would have the boys making so much money that they could support him for the rest of his miserable life! The boys are 9 and 11!
A lot of what I post comes from real life situations of people that I know, so please take what I say with a grain of salt. I have no statistics or research facts to back all this up....just the experiences of people like us.