I can think of plenty of other countries and for me it’s not a cultural we’re better than them thing. Most of the unique attributes of British English (like this issue with subject-verb agreement) only developed during the second half of the 20th Century and only in the UK itself. This means that these matters of usage are unique to Great Britain and not to the entire commonwealth and former empire (Australia, New Zealand, South Africa, India, etc). This means that even though these countries may have a variety of English that has much in common historically with that of the UK that in fact the special BrE forms are not part of their usage.
From a standpoint of linguistic study, the English of the UK is facinating compared to that of the US/Canada which comes off as quite boring really because its so similar from place to place. North American English is very standardised with only slight differences in pronunciation and some regionalism. Nowhere on Earth however has more disparity in dialects of a single language as does the UK. There is so much difference between the pronunciation, vocabulary, grammar, and even chosen forms in the UK. The differences are geographic with Newcastle and Essex sounding as if they are totally different languages sometimes, and even within greater London huge differences exist. The differences are also social and economic with different classes of people having vastly different varieties of English – but all within that family of BrE. From a teaching standpoint this creates an issue. Do you teach RP English even though barely anyone actually speaks it? Or, do you choose a particular UK variety that is common and teach that? Do you teach students to omit the letter ‘t’ in the middle of a word or to add some other common attribute that a certain group in the UK uses (but that others don’t)?
The way I see it, you have 20 million native speakers in Canada, 315-320 million in the US, 5-10 million in Mexico, 20-30 million in the Philipines, and various others in the Caribbean and Polynesia for whom North American English is their variety. It amounts to over 75% of English speakers speaking one variety that is very stable and similar among its speakers versus 12% speaking another variety that is very different from one speaker to another and which has a much looser grammar and vocabulary.
Really, if we want to go toward teaching a variety of English that’s not North American, we should be teaching Indian English which is second to NAE. Even then, Indian English has been moving steadily closer to North American English in usage of vocabular, grammar forms, and pronunciation.
The other argument to consider is that any British English speaker can understand NAE, but many non-UK speakers don’t have a clue what a lot of BrE forms mean.
So you see, it’s not a cultural debate, it’s one of logical selection of which one to spend classroom resources on: Standardized form used by 75% of Speakers versus non-standardized form used by some of 12% of speakers?