I think they did start using the British cover eventually, but with the American title. I've never understood why they changed the title either, I know a while ago you could try to justify it by saying Americans wouldn't read something about London, but after Harry Potter and Dr. Who I don't think that would be the case any more.
I'm happy to say that they did (my copy is a newer one, original cover art but with the American title, so almost right), and the other books in that series are using their original cover and title. I think I would be okay with them not changing anything, and just leaving punctuation and alternative spellings intact. At this point I've read enough Doctor Who novels...other adult readers should be able to cope, one would hope.
Maybe they were afraid people would think it was a geography book?
I wish I could get paid to make decisions like this. I would love to get paid lotsa money to make completely mental, insane, baffling marketing choices. I believe I would be ace at it; I'm already mental, so I'm halfway there.