Unless, of course, you consider the rest of the world. In India English is an official language and they spell things in the UK way. In fact anywhere I've ever seen international English used the UK spellings have been used unless they were specifically dealing with Yanks. I don't know about all of China but I wouldn't be remotely surprised to find out they use the UK spellings when corresponding in English, given the Hong Kong connection. Singapore/Malaysia uses the UK English as well. . . .
Hey, I'm half American and half Australian so I don't really have a horse in this race (or perhaps I have two) but the provincial attitudes of some Americans when it comes to language and dialect differences is annoying.
The wikipedia statistics above were for native speakers.
I live in China and have spent most my adult life in a Mandarin/Hokkien language environment. Spellings and usage here generally follow the US, but very few people could even be considered to be fluent speakers. Hong Kong does still use UK spellings, but Taiwan and Singapore have considerably more US (and in the case of Taiwan, Canadian) influence. Japan and Korea also favor US spellings. So do Mexico, Guatemala, Nicaragua, Honduras and a lot of other places you may never have visited.
Maybe you see the attitude as "provincial" because you haven't seen much of the world yourself!
In any case, from a purely pragmatic view, the US usage is standard. I know the minority of native speakers on the other side dislike it, but let's face it. Just about everyone on earth is exposed to Hollywood and US television. Even in former UK colonies such as HK or India, North American usage is widely understood. The same can't be said for Irish/British/Welsh/Australian dialects.
Hey, I'm half American and half Australian so I don't really have a horse in this race (or perhaps I have two) but the provincial attitudes of some Americans when it comes to language and dialect differences is annoying.