Being in college is a time to start branching out on your own without depending so much on your parents, but let's face it, the Scoobies were on their own much earlier than most kids their age. They were privy to the scary underworld of Sunnydale, which their parents didn't even WANT to know about. Even Joyce, who was the kewlest mom I've seen on TV, didn't know what was going on for quite a while - and she was better off that way in the beginning. Would YOU want to know that your daughter risked her life every night, fighting demons and vampires, with the very real threat of her not coming home, ever? I think that Joyce was the exception - Buffy DID eventually tell her, but the other parents weren't anywhere near ready to accept this kind of a lifestyle. Hell, Willow's parents wouldn't have been able to accept any of her choices, even the more realistic ones, like her sexual preference. The show is better without their "real life" lectures - don't we, as fans, get enough of that as it is?
Just a thought.
Midge
The Godess, Herself