Someone may have said this already, but I think it is needy parents who are the problem, the "helicopter parents" who relive their youth by sitting on their student offspring's shoulder at Open Days, settling in, Freshers' Week, first week of lectures, forever descending on them at weekends, skyping them at every moment etc I remember somebody on GN who either said she did this or recommended leaving the laptop on for all-day continuous skyping because she missed her DC so much when he/she went off to college. 
Let them grow up, teach them to be independent, NOT to need you (hard!).
Another anecdote I heard recently was about a Mum who cooks all the meals for her son and DIL and takes the food round for them to microwave " because DIL is pregnant" , not suffering from pre eclampsia or ill, just pregnant. And not just the odd casserole or cake, all their meals.
Of course I snivelled all the way home after we took each DD in turn to university, but they went off happy and ready for independence.