There are really only a few reasons that "world class" cities, or redefined, large cultured cities, are better than small cities:
1) Culture - If you make a point of it, you can see some really great art in NYC every day and never run out of new exhibits.
2) Convenience - Things are open late and every store under the sun is within 30 minutes.
3) Jobs - For certain industries, you need to be in a top city to get to the top, if that is your goal
4) Food -...