I think that's fine for the families who are in Senior exec situations but what if you can't afford private education?
I can speak to my own experience with my kids and now that they are through their international education. They had elementary school in the US, and jr. high and high school in the UK with a year here and there in Canada. In the US, they focused on Reading, Writing and Arithmetic and not a whole lot else. This gave them an extremely strong foundation so that when they got to the UK, they were able to pick up the content easily and fly. I loved the state schools where we lived. My DD did her A-levels in the UK and my son did his GCSEs. Upon returning to Canada, DD got in to her first choice uni and was given credit for her A-levels so three less courses she'll have to do in order to graduate. DS was able to go to Uni a year early as his GCSEs and two high school classes in Canada, gave him enough for admission. That's not necessarily right for all kids to go to Uni at 17, but for him, it's been a very good thing. The fact of the matter is - their education did not suffer at all having moved around. In my mind, the combination of systems only enhanced their education and gave them a much better overall education than if we had stayed in the same system their entire lives.
All universities have international admissions and that is what you need to keep an eye on - what they'll ultimately need to gain admission with the education they've received. They may not need to do American exams to gain admission; it depends on the institution. My kids were admitted to Uni as International students but they are home students for the purposes of fees.
Honestly, the most difficult part of the whole process was ordering the darn transcripts!