Thanks for the reply Dell. That is the understanding we have of the US tax law as well. I remember the first time I heard that I could be taxed on my overseas income I was outraged! But I think there is a minimum amount that you avoid double taxation on. Not sure what the amount is now but I recall it being about $70k US a number of years ago. The US did not tax you on the initial $70k of your foreign earnings (earned while living in another country) but then some US tax would kick in for earnings over that amount.
Of course I could be completely wrong in my statements above! I am not a tax professional and would never pretend to be. I'm just trying to get my head around citizenship and taxes.