Hello Mike in Japan-

Arguments claiming American English to be a “dumbed down” or “lazy” version of British English are based on the erroneous premise that American English is a perversion of British English. Any real linguist will tell you that modern British and modern American English BOTH evolved from a common source, the pronunciation of which was quite different from either modern variant. Your argument seems to claim that British English is somehow standardized and has not changed over the years when in reality that today it is just as different from the pre-colonial English as American.

In fact, most scholars point to a phenomenon known as ‘retention’ in which the colonies actually retain the linguistic styles of the period of colonization while the original homeland, because of international influences, changes rapidly. There are many examples of grammatical structures and vocabulary that are very common in the US that are considered archaic and old-fashion in the UK. For example Americans use the past-perfect form of “to get”, which is “gotten”, a conjugation that has not been used in England in almost two centuries.    

You must also remember that English is very different from other languages in that it is used by several extremely influential countries. In contrast, although the former French colonies do produce notable literature, almost all cultural expressions in the French language come from France—which is why French can claim to have one standard. In the same way, Japanese can claim one standard because Japan is the only real source of Japanese literature and culture.  But because both the USA and the UK produce vast amounts of literature and film, thus generating substantial cultural accomplishments in both linguistic variants, it would be impossible to dub one or the other as incorrect.

Another thing to remember is that English, while it does have its variants, is much more uniform than other international languages like Arabic or Spanish, which can differ greatly from region to region and even have entirely different verb conjugations. 

In conclusion, I would argue that you must take into account that English has official status in 6 very influential countries, each of which can claim a substantial body of literature, and therefore cannot be compared to Japanese which is only spoken in 1 country and thus can claim one standard.

Carl