Those things get put in as conditions when developers need variances from existing zoning or specialized PUD's and such, not when they submit a plan that conforms to existing zoning.

The developers are already on the hook for sewer hook ups, streets, sidewalks, water hook ups curb trees and other infrastructure required be the zoning laws.  

You don't get to steal extra money from a developer just because your city staff didn't anticipate ten years ago what the future would be.  You are stuck with what they draft and get approved.