Perhaps I should clarify that "demanding American spelling is unreasonable" was specific to the context of HN (or other open discussion forums with international readership).

Within say, the volunteer-maintained documentation of MDN, the tradeoffs are quite different. There, ease of reading for reference by busy coders is much more valuable relative to ease of typing up a new contribution. Frequent switches between "color" and "colour" become a time-wasting distraction.

MDN should pick a standard and insist on it. And if Ubuntu chooses to require British spelling throughout, I'd say that's good.