Is it really? Your argument was that you spelled it Brighton because of the pronounciation. That's where I would say local dialects factor in.
To my knowledge it's not a matter of grammar. Or is there a rule somewhere in the English language that covers such a case?
Please, don't be offended by my asking. I'm totally serious here, since I'm not a native speaker and you tickled my general curiousity in languages with your comment.