Despite a number of posters on here saying they moved hundreds (or thousands) of miles away and claiming they have a massive support network around them where they are. I think they are the exception rather than the rule.
I know quite a number of people who have moved hundreds of miles away from family, and they really struggle. Because whilst on Mumsnet, people claim to have a massive support network around them in the new area they moved to (100s of miles away from their family/friends;) in real life the vast majority of people I know who have moved a long way away from family don't really have anybody/any help/any support. Or if they do it's very little. And any support or childminding they do have, they have to pay for, like creches and nurseries.
Seriously - in the vast majority of cases, random new neighbours and friends that you have not known for that long will not be looking after your kids, while you go to work, or go out socialising, or if you're in hospital...etc... People can claim that their new neighbours around them are quite happy to act as family, but the reality is, that in the vast majority of cases, this won't happen.
I have known my neighbours around me for the ten years I have lived here, but like fuck would I be looking after their children every time they go to the pub, or while they are at work. I spent over 20 years raising my own 2 children, and no doubt will be helping them with their children sometime in the next 5 to 10 years. So like fuck would I be babysitting the neighbours children!
The reality is (despite claims from certain posters) that the vast VAST majority of people will not be prepared to look after your children. Only family will do this. And don't bother saying 'not everyone is as mean and selfish as you purplebutterflywings,' because it's true. MOST neighbours and new friends you make, are not gonna be your onsite babysitter/childminder. They have their own lives, and their own responsibilities. And in many cases, either their own children to look after, and/or a job to go to!
I know far more cases of people who have moved far away and have nobody to help them/no support, than I do people who move far away, who have a massive support network. In fact, I don't know anybody at all who's moved far away from home who has a massive support network. They pretty much all struggle. And as a pp said, their children are growing up with no family around them. No grandparents, no aunts and uncles, no cousins. How sad. 
I have travelled a lot, with DH, by myself, and with DH and the kids, but no way would I ever have moved 100s of miles away from my family and friends permanently.