Anyways, you claim that your definiton is the "accepted definition", but I have to ask "by whom"? Certainly not bookstores, I know that. They don't even treat Science Fiction and Fantasy as different at all... Certainly it doesn't seem to be the definition I see used in common discourse. When someone says "Science Fiction", they usually mean "robots and spaceships", not "cavemen learning how to use bows".
Also, if Science Fiction has such a clear definition, then what is the equivalent definition for Fantasy? These are two terms that always go together, serving as two sides of the same coin. If you want to seperate them at all by genre boundaries, rather than setting boundaries (where the line is fairly distinct), you need to give a good definition. If you can make a claim that Star Wars is Fantasy, but not Science Fiction, what definition are you using other than "it is kinda like Science fiction, but it doesn't meet my definition, so it is Fantasy"?