Let’s see if I can make this clear while being reasonably polite. First of all, note that I do not claim (though I could) that American English is the international standard, only that it is becoming a standard, alongside the older UK standard. Because so many people use it, it is important to understand its peculiarities.
When most English speakers were part of the Empire—or later, of the Commonwealth—British patterns of spelling, punctuation, and usage prevailed. Now we live in a different world. Chinese from Hong Kong and Singapore speak with a British accent for good historical reasons; but enormous numbers of them from Taiwan and The People’s Republic study mostly American patterns. Arabs from the Middle East, Japanese, Russians, Central Asians of all sorts, and hosts of other people study much more often in American colleges than in British ones. When treaties are being negotiated, international statements issued, meetings translated, and films dubbed, the lingua franca is far more likely to be American English than UK standard. American television and movies have alone spread American accents to the four corners of the globe.
This may be a deplorable fact, but it is a fact. Like many Americans, I warmly admire traditional English speech patterns and accents. This site in no way suggests that American ones are superior. They are simply more prevalent, in the world at large, and certainly on the Web. I am not an expert on UK usage.
It is also worth noting that in a surprising number of cases, American pronunciation and usage are more conservative than that of the British. Some instances are noted on these pages in which U.S speakers preserve older patterns abandoned by speakers in the British Isles.
My goal is to defend American standard usage from the bullying of non-American critics, and to warn Americans not to be parochial in assuming that everyone speaks like they do. For obvious reasons, careful writers have to pay attention to a relatively small number of differences; but we don’t have to let those differences whip us into a frenzy of mutual denunciation.