Your question is perfectly reasonable, Brian. I do expect my UX to be informed by my choice of locale and language. In fact, a lot of people feel that way.
My issue with Outlook.com's yomi name UI is a product of two intersecting factors: They are unneeded by the vast majority of Western users (in my estimation), and they appear at the top of the dropdown menu. At the very least they should be moved
to the end of the list for users with both a Western locale and language.
Noel made a great point though. America is a giant country with a single postal system, so it's easy to forget that the rest of the world is a much more diverse place. However, I think it's worth noting that most (if not all) of Noel's examples already
work with the existing Live Mail address book structure. Nickname, first name, last name, postal code, province... these all take care of those use cases. I put Dutch common names in the nicknames field and drop most Spanish legal first names entirely. And
with regard to Icelanders, Noel meant they don't use family names as a surname, even though most of them do use a p/matronymic surname after their given name.
I've never had a need for yomi names in my address book, if only because I can't type the damn things, so I just attach a scan of the business card in the tiny subset of cases where it's needed.