I don't think that it is a matter of prejudice.
I think rather that it's about the fact that no matter how fashionable she is, the Queen of Jordan is not going to be as high profile as the first lady of the United States or the wife of the French President who used to be a super model. Developing leaders themselves get so little press so think about how much press their wives get.
I think that the only reason why she gets as much international press as she does (Vanity Fair, Vogue etc.) is because she herself works on so many international issues and attends these high profile events like the MET costume ball etc.
For all we know, the wife of the prime minister of Sri-Lanka is a fashion icon, but we'll never know it because no one cares about Sri-Lanka enough to cover what the first lady is wearing.