This is interesting, we've had these discussions recently as DH was contacted about a job in the middle east. It would have been great money, great lifestyle, but he didn't get the job.
We thought in terms of how our families might react, and assumed my parents would go into slight meltdown at me 'taking DS away' (and the new baby, I'm pregnant and we would have moved before it was born), i think DH's parents would have been very upset but be excited for us. I think it helps that both sides have enough money that we know they could afford flights a couple of times a year (we'd agreed we'd have to hav 3 bed place so we could put the two DCs together when we had guests).
However, neither of us thought about missing them as a reason not to go. I really don't think I would miss them that much. I worried about my friendship network, having a new baby in a country where I knew noone, but then I moved here when 7 months pregnant, and have built a network of friends in that short time so am relatively confident I could do it again in another country amongst an expat community (plus DH is more confident/relaxed as he has lived abroad before, albeit much closer in Europe and could and did pop back for weekends).
Mind you, neither DH or I are only children, both of us have DBs who live closer to our respective parents than we do (although for BIL, it's only about 15 minutes closer for him than us and he works longer hours!), and both sets of parents are very healthy, so it's not like we'd be leaving elderly, infirm parents on their own.
If DH got another great job offer overseas (he's recently been headhunted for a job in HongKong but turned that down as he didn't like the job), I don't think we'd let family and friends hold us back if it was best for our little unit. That might make me selfish, but I also would hate to think that DS when he grows up would turn down opportunities just because i'd miss him...