Well, My 5yo eldest is very sociable and can strike up a conversation with pretty much anyone. My 3yo is very much happier with her own company than Dd1 ever was. But then, she's 3, so there's all sorts of development things happening with her in just learning the basics anyway, which would happen anywhere.
My own feeling is that learning to be sociable and interact with their own family is the priority, and more useful than learning to interact in an artificial age-peer environment like school.
My other strong feeling is that it's important to define what we mean by 'socially adept'. Do we mean shyness? If a child is shy by nature, being in an age-peer group isn't neccessarily going to do anything to change that, and may even ingrain it more.
Do we mean able to hold a conversation with someone else? There's no reason why school or home should have the advantage on that issue. Do we mean knowing about the latest trends/fashions/obssessions? Well, hands up, my girls don't know about those things, and I wouldn't call that being socially inept, anymore than I am because I don't know the in and outs of the latest Coronation street storyline
When there's other people around, my children don't sit in the corner rocking backwards and fowards murmuring the periodic table to themselves. They're generally polite to adults and other children, but they're not automatons.
So I suppose I would say that when people suggest that HE kids are more socially adept, I would want to qualify that with - there's nothing kids at school get, in terms of positive social interaction, that HE kids can't get too, but there can be social interaction that HE kids get that schooled kids don't. All depends on the kids and the parents, really.
goodness, it's almost like we're all individuals or something...