What's wrong with English education in this country.

Yesterday, in class, my co-teacher writes the word "marvelous" on the blackboard. He asks me, "is this spelled correctly, or are there two Ls?"
I tell him that both are correct; he's written the American spelling, though Australians spell it with two Ls.
"Oh," he replies, "I suppose the American spelling is better."
WHY is American English so much better? Just by sheer force of numbers? In that case, do all Spanish students learn Mexican Spanish? This is becoming another rant, but I should like to think that students of a foreign language should learn a sort of internationalised version of the language to enable them to handle variations of the target language. They don't have to use one particular kind of English or another, just whatever is understandable. I tell my students, that as foreign speakers of English, they can say mum or mom; mobile or cell; bog or restroom - whatever they want. So when I hear that students who write words like colour, programme or marvellous in their exams will be marked as wrong... well that's bloody stupid.