I thought the bedrock is pretty high in new york, so you don't have to go down deep unless it's for rock anchors. For example, 1WTC in New York sits pretty much on bedrock. You don't have that condition in Chicago.
PT construction is the standard for high rise residential construction in Chicago. You can curve the tendons to avoid conflict with conduits/pipes/etc.
Allows for less reinforcing in the slab, resulting in thinner slabs and the heigher floor to ceilings people want in residential buildings.
An easy way to tell where bedrock in NYC is look where all the tall buildings are. Southern end of the island and middle.
Those are for the carpenters installing the decking to tie off to as a means of fall prevention. If you go there during a day they are placing decking, you will see the carpenters tie off to the poles.