I think you misunderstand my point. I am not saying defiantly that American is a different language to English. I am saying that I have no idea what is the correct definition of "language" (although
Dictionary.com defines it to include "the system of linguistic signs or symbols.......any set or system of such symbols as used in a more or less uniform fashion by a number of people........any system of formalized symbols, signs....." which effectively means that if you use letters as the symbols, they have to all be the same spelling).
However all languages have "rules", and if you don't stick to those "rules" you are, by definition, at best ignorant, and at worst illiterate. So if we say that the language used in the US is English, then you are saying that the correct spelling in the US is the English spelling, and spellings like "color" and "ass" are incorrect spellings. Since all Americans use these spellings, this means that, if Americans speak "English", then all Americans are idiots. That is why I prefer to believe the option that Americans speak "American" rather than "English"!
As an amusing(ish) post script: Dictionary.com is an American site. When I spell checked this post, my spell checker (which is set to "English") objected to their "incorrect" spelling of "formalised".