Firstly, as I routinely highlight on this very blog, those three words represent a mere fraction of the vast array of American English spellings that differ from their British counterparts. Many Brits might be surprised to learn that there are, in fact, hundreds of these kinds of spelling differences.
It has long been my position that American spellings are not only permissible from a historical point-of-view, but from a practical one. Unlike the oft-seen example of someone (on either side of the Pond) incorrectly using there as a possessive, spelling variations in this sense don't themselves alter the meaning of a sentence. When an American writes the word honor, it is clear that the definition is exactly the same as when the British write honour.
Moreover, it should be noted that American spelling variations often align better with a word's pronunciation than do their British counterparts. Indeed, this was the idea of 19th century American lexicographer Noah Webster, who popularized hundreds of US spellings with his An American Dictionary of the English Language.
However, the primary reason I choose not to take issue with US spellings is simple: I don't want to be a hypocrite. After all, something often overlooked by British detractors of American spellings is that we ourselves have made similar amendments to the language over the centuries. Take, for example, the word November. Just as the Americans opt for -er at the end of centre, so too do the British (and the Americans) with the old french word Novembre.
In other words, language is a constantly evolving thing - a fascinating network that takes on a life of its own. As consumers of language, I believe we should celebrate these changes, not deride them. After all, how many of you, for example, can honestly say you recognis(z)e the phrase below?
Believe it not, séo ealdspræc was once an English phrase (old English, that is) that could more or less be defined as the history. Some of us would do well to learn the history of language before taking an admittedly tongue-in-cheek swipe at our American neighbo(u)rs.