“I don’t get this. Aren’t UK taxes MUCH higher than U.S.? Especially at her level.”
No, the UK is very popular with the super-rich because we let them keep most of their money:
http://www.guardian.co.uk/society/2012/feb/24/why-super-rich-love-uk
But it's different in the UK. Here, if you come from overseas, and can prove strong links with overseas, and can prove that you are going to return to overseas, and can therefore establish a "domicile" overseas that is different from your "residency" in the UK – well, in that case, you are treated entirely differently for tax purposes. You pay tax on your income in the UK, like the rest of us; and you can remit capital to the UK; but your overseas income, as long as you keep it overseas, is out of the reach of the Inland Revenue.
What this policy amounts to, in practice, is that the UK has a gigantic sign hanging over it saying, "Rich People! Come and Live Here! You Won't Have to Pay Any Tax!" It is an extraordinary policy for any developed nation, and not one that anyone else has been tempted to adopt. Other countries have low tax rates to attract businesses – in the EU, Ireland and the Netherlands stand out – but the only countries that have anything even vaguely resembling the British policy towards the super-rich are places that are openly accepted as tax havens, such as Monaco and Switzerland.
America's tax policy is despicable and consequential.