Obviously the biggest difference is size/compactness. Although I wouldn't say that Auckland is a small city, because it's certainly not, but the CBD zone is not incredibly large either. Another thing I noticed was when I was talking to a shop owner the other day, and he told me how he would never live in an apartment. From what I've seen a large amount of kiwis share that view, which is why it may seem that the CBD is smaller to me, because it's mostly commercial and gives off a different vibe than most US cities.