NYC's and LA's in-city sububia and Chicago growth

Here's one I just can't seem to get a handle on. Thought I would throw it out here and see what you folks think. Both NYC and LA are structured far differently than Chicago. Due to their physical size and lay-out, these cities create a much wider city-to-suburban environment within their city limits than Chicago which is basically city with a small suburban fringe within city limits. New York does this through having the outer boroughs that include relatively sparsely settled Staten Island and the outer reaches of Queens which are basically suburban. LA doesn't have any political divisions, but the geographical ones are most evident. The San Fernando Valley, a part of the city, is removed from it by mountains and is largely suburban in nature. Both NYC and LA are growing cities, and most evidently so. Their rate of growth exceeds Chicago's. Future growth projections for both are impressive. All three cities have done a great job of attracting immigrants, the largest source of growth in any of them (without immigration, all three would be losing population). My question is this: is it the physical layout of NYC (outer boroughs) and LA (Valley, other underdeveloped areas) that keep their rate of growth ahead of Chicago (a more traditional city with little suburban land within city limits) -or- are they more attractive for growth than Chicago? I suspect the second might be true (although I would hope it isn't) insofar as Cook County would represent a greater Chicago similiar to NY and LA and the county is not experiencing growth.>