I can't help but wonder if those advocating distance are the same people we hear bitching on the Family Relationship threads about how shitty their parents are and how much they hate o be around them. Cause or effect of leaving at 18.
I don't think leaving at 18 has anything to do with how close you are with my parents. I was the pp above who grew up in Chicago and went to school in the West Coast and now live far away from my family, and I am very close to my parents. We visit a few times a year and I talk to my mom on the phone nearly every day. We just have a family culture that doesn't rely on geography to stay close. It has always been my family's philosophy that you live where you have the best opportunities in life: educational and professional. In my case, there was a school that was a really great fit for me that happened to be on the West Coast. Part of this, I think is that my mom was a military brat whose mother immigrated from another country, so moving around has always just been taken as part of life.
My SIL went to school a three hour drive away from home and she doesn't get along with my MIL at all, so I think there is really very little correlation.