I believe it's because no other member of the royal family is identified in such a manner.  On the other hand, we have no other articles on current spouses of other royal princes.  HRH The Duchess of Gloucester, HRH The Duchess of Kent, and HRH Princess Michael of Kent do not currently have articles, nor does HRH Princess Alice, Duchess of Gloucester, the late HRH Princess Marina, Duchess of Kent, or any of the wives of Victoria's younger sons... That means there's no real precedent, no?  23:41 May 10, 2003 (UTC)