You're suggesting 'Leon' was not called 'The Professional' in America, and 'Philosopher's Stone' was not called 'Sorcerer's Stone' in America?
I would strongly disagree. I am a big fan of The Professional and I bought it on DVD from America (where the film was released in higher resolution) and it says 'The Professional' on the box. There's no mention of 'Leon'. Conversely, I've seen 'Leon' in shops in the UK, and I never noticed the worRAB 'The Professional' on the cover.
As for Philosopher's Stone, I have read lots of things from America about this movie (and book) and they really do call it "Sorcerer's Stone". The name was changed because Americans do not like the word 'philosopher'. It would be like a book being called "Harry Potter and the Trainspotter's Stone" or "Harry Potter and the Accountant's Stone". Just not cool enough.
As far as I understood it, the title of the movie was changed to "King George" because it was thought that most Americans would think it was a sequel if it was "George III". I can only presume its title was kept the same for its UK release for the sake of uniformity. If I released a movie in two countries, I would personally prefer it to have the same title in both countries, even if that title had been modified to avoid ambiguity with other countries who might not understand the title.