Momtomom you are right that Brits do have networks of friends that start at a young age and continue throughout their life, I have school friends, uni friends and mum friends all nearby. This is simply because England is small!! Even when i meet new people there is often a connection, for example, one of my new mum friends knew my husbands family and had been on holiday with them at a young age! It happens all the time.
When I lived in LA it was different, LA was a melting pot of Americans living miles from their families in Dallas, Washington, NY etc. also, in their college years they would travel huge distances from their families then end up working in a different place again breaking ties each time. I think this encourages friendliness as people are perhaps more sympathetic to newcomers.
I think it is unfair to criticise out culture and especially to take one woman and use her as an example to tarnish us all with the same brush. As mom to mum said its not wrong it's just different.