The bigger family IMHO helps. If something happens in the UK then you know there are 4/5 other siblings there to be on hand whilst you're travelling. No-one's on their own.
As an only brat then I'm very very aware that should anything happen to either of my parents then the other one is going to be sat there on their own for 48 hours until I get back.
My wife is one of 3 with lots of close cousins (Devon connections, what can you say ;-) ). She's managing OK via skype and much that it pains me, then Facebook.
So that' doesn't
help in as much as pointing out that someone else may be in a worse situation, but the overall point is that it's an issue that faces everyone who moves. It's a real issue, and there's certainly some that don't thrive with that physical separation and end up moving back. But there's many that do stay. As far as I can tell on the forum over the past few years then the biggest factor is how many connections you make over here, and how long it takes ot build that network of friends / support over here. Not how many / how close the bonds were in the UK.