I came from a culture where parents don't let go ever and literally become a millstone around their kids neck even after marriage, especially for boys. The younger generation is changing but the older generation has no incentive to change since they feel that "I have paid my dues to my parents, now it's my turn to get it all back". Many marriages (of the children) are ruined because of this parental obsession, refusal to let go, and need to control children.
I believe the reasons for difficulty in letting go runs the gamut. On one side, it may be just purely love and longing. On the other side, it's a need to be compensated for all that has gone into raising kids - mostly unstated and subconscious, but nevertheless there. Not compensation in materialistic terms, but compensation emotionally as a way to validate our existence, live vicariously through their experience and success, and whatever else we carry deep within.
As a reaction to the excesses I have seen in my own family (not my current nuclear family but the family I grew up in), I developed my own philosophy.
The Children should be treated like orchids, not vegetables. Orchids' sole purpose is to be there and beautiful. The only enjoyment we get from them is to appreciate their beauty. Compensation for all the care and fuss that go into nurturing orchids is the right to admire it from a distance and knowing that you have something to do with creating that beauty.
Vegetables you grow, on the other hand, you can eat and nourish yourself with. For the evening meal, you pluck the tomatoes and cut the leaves and make a salad. In short, vegetables have a utility, and you, consciously or subconsciously, expect them to be "useful" to us. That utility does not have to be physical or material. The utility often takes the form of validation of our existence, affirmation of our values, confirmation for all right things we have done, a means for us to live vicariously, a way to absolve of ourselves of our past sins and wrong, and even a filler to stuff our emotional void with. This utility runs the gamut: on one side, just a need to be close emotionally, and on the opposite extreme a need to control the children (you should become a doctor, or else I am not paying the tuition!).
In the culture I grew up, this "utility" was very often blatantly demanded of the children. In the culture I live in now, I believe that often it is done very subtly and mostly subconsciously on the part of the parents, but I believe it's still there, perhaps in a low dosage form - maybe even more difficult to deal with since it's not stated openly.
I am very acutely aware of my own needs, and am constantly second guessing my own motive when I steer my kids one way or the other: Am I really doing this for myself, or am I doing this really for their own benefit? Often enough, I have to say, the real motive is not 100% selfless.
I vowed to treat my kids as orchids, not vegetables. And, so far, with freshman S1, I have been doing OK. I have let him dictate the pace of our communication according to his needs and wants. And, he has rewarded me with 3-4 phones call a week to us, and 3-4 rather thoughtful email exchanges a week.
That said, one thing I always strove to instill in my kids is the sense of appreciation for other people's good will and the awareness that they are not just a product of their own genius, but rather a result of good will and good deeds on the part of a lot people who helped them and loved them. A wonderful woman took care of my kids (both of them) for 14 years full time. I consider her by now a family friend. In the last week before S1 left for college, I advised him to take her out to the best restaurant in town and pay for it with the money he earned during his internship in the summer. She stopped by after that, and the look of unabashed joy in her face was priceless. Later that week, he took me, H, and his younger brother out to dinner and insisted on picking up the tab.
Who knows, if I am really lucky, maybe my "orchids" will be "edible flowers"