Writing in the appropriate English

Today, I read a story over at Dispatches that got me thinking about using the appropriate English in writing. In that piece, the Mr. Brayton block-quotes an author with the London Telegraph who quoted Obama campaign insiders as saying (emphasis mine):

"We're much stronger on the ground in Virginia and North Carolina than people realise."

and

"The poll numbers say Florida's back in play. McCain hasn't spent a single penny there and that's Obama's calculation, that he can capitalise on that."

Now, I'm being picky here, but should the author not have written, "...than people realize" and "...the he can capitalize..."? I know this may sound petty, but to me the spellings, "realise" and "capitalise" are British Commonwealth spellings. The words "realise" and "capitalise" are therefore not spelled correctly in United States English. Therefore, if you are directly quoting a person who - I am presuming - is a United States citizen, why intimate - through the choice of English - that he is a British Commonwealth citizen?

Similarly, it really gets my goat when newspapers in the United States talk about what "the Labor Party" does in the UK. Of course, there is not "Labor Party", but a "Labour Party" (the CAPITAL letters indicate that is is a name, and as such, should be spelled in the manner it is written by the named person/organization/etc. - why else would Catherines, Cathrines, Cathrins, Katherines, Kathrines, and Kathrins be vigilant about how their names are spelled). In the course of things, I feel that this is a more egregious error than the one committed by the writer in the London Times. However, this brings up an interesting question-de-minute for me: to what extent should a person write in the "appropriate" language and dialect? For example, at the language level, if I were to be paraphrasing a person from Mexico who was describing "pezes" in an "arroyo", should I translate it to "fish" in a "book"? The word for fish (pez) is not one used widely in English, and might be confused for something else. What about "arroyo", though? Does it carry a specific feeling of contextualization that I might therefore choose to leave it as the Spanish word (which also happens to be used in the Southwestern United States, too)? Or do I remain a purist and change both words? I don't know.

For a dialect example, if I were to be paraphrasing a person talking about small rivers in upstate New York state, I wouldn't use the word kill, but use a more widely used term like "stream" or "creek" or "brook". However, if the person said "kill", should I not use that word instead of inserting my own for clarification purposes? (Similarly, if someone describes a draw, wash, gulch, gully, etc.?)

These two case of British vs. U.S. written English, though, is more nuanced than either of the two examples. There are words (not too many that spring to mind) where both the spelling and pronounciation differ significantly enough between the two Englishes that I feel it does warrant spelling it in the manner of the person speaking. One example that springs to mind is aluminium vs. aluminum. (Check it, there is a difference.) However, both "realise" and "Labor" sound effectively like "realize" and "Labour" to make the difference only in writing. Thus my dilemma. As a purist, I would say that writing "realize" when spoken by a U.S. English speaker is the correct thing, even though the publication is otherwise in British English (it is, after all, an indication of how the person spoke). The pragmatist in me says that one should write in the English required of the publication (thus even negating the difference between aluminium and aluminum).

I don't think there is a "right" and a "wrong" on this one. It just irks me when I see it, and then I get irked that I got irked. (Finally, I just got irked enough that I decided to write about it, I suppose.)