AOL has never fully departed from their original design...an online service.
Online services were all most people had in the old days, back when many people wanted to upgrade to a 486. There was no such thing as the "World Wide Web". Al Gore hadn't yet invented the Internet, so there was no such thing as an Internet Service Provider. And online services like Prodigy, Compuserve and AOL made people feel as a part of a community.
Some people like having a central UI entry point for everything that matters most. Why do you think Microsoft came out with the MSN Explorer? MS realized people actually like this...otherwise, why would well over 28 million people use AOL? (yes, I'm aware the AOL churn has taken their numbers down as of late...)
I'm not defending AOL, I realized how stupid I was in '94 and quit. I especially didn't like hearing about v5.0, and I'm really glad I missed that debacle.
But I am defending your parents. They are comfortable with their "life choice", and you should accept it and love them for who they are, and not criticize them or try to change them...as I understand it, they've probably been inclined toward online services since birth. It's nothing to be ashamed about.