I do not remember who represented the US at the [first] Wales wedding, But one of the first ladies was at the Diana funeral, as I recall.
The Commonwealth states are perfectly understandable. and any of the Arab princes would, IMO, be those who are personal friends of the family such as the Sultan of Brunei. [I know, not an Arab, but still a Moslem and a good friend of the Wales.
BTW, I have been told, quite recently that the Duchess of York was "consulted" about attending, as her daughters are part of the wedding party, but it was mutual, she did not expect to go and had other plans anyway. I can see that- she did not wish to distract attention form the bridal couple. I hope the rest of the royal rabble behave with such dignity.