The specifics here are that the New York skyline was originally two big textures covering two faces of the skybox. Late in production, to save video memory they

The specifics here are that the New York skyline was originally two big textures covering two faces of the skybox. Late in production, to save video memory they cut one texture and replaced it with a mirror of the other one, of course cutting the side with the towers so that they wouldn't show up twice. (Source is an old IGN interview that I hunted down ages ago, because every time this trivia shows up somewhere there tends to be a comment war about how removing a building from a skyline couldn't possibly save memory, blather blather.)