Parents who are too involved can be just as much of a problem, but that's really the minority. I had friends, too, where we'd always hang out because we knew we'd never see the parents - some of them turned out really well, and others ended up with things like DUIs and drug charges.
And with the relationship thing, there are exceptions to every rule, like you said. It's so impossible to make generalizations, but the bottom line is that your relationship with your parents will always shape the way you go about relationships for the rest of your life. "Good" parents aren't always successful, and that's not always their fault - "bad" parents can raise a very successful child and they may have had no beneficial influence on the outcome.