Some people have been asking why the first premiere was in London, rather than the more obvious choice of New York. New Line, the studio behind the film, have said the decision was taken simply to maximise the movie’s ‘global appeal’.
With foreign box office now as important as domestic grosses, it could be that they want to give the film a foreign marketing push first. This was partly the reason a film like Spider-Man 3had it’s world premiere in Tokyo last year.
Another factor could be that because New Line sell off distribution rights to foreign exhibitors (in the UK, it is being released by Entertainment Films) and they get a say in when to stage the premiere.