Well I think the reason its Concourse 4 and not D is that it was announced prior to the renaming. It would def. be renamed D as construction work progresses. There was also talk of making it a Terminal 4 with a separate check-in area but I am not sure if that will take.

Terminal 3 and concourses B/A are physically separated by an active taxiway. I know what you mean by there is no tunnel like T1, it is done quite cleverly. The road descends below ground as you approach the entrance to the terminal so you are already underground. You do the long walk from Chauffeur drive drop-off to immigration/security and up the escalator.