It seems reasonable to me that an Obstacle Departure Procedure would include more "strict" rules (steeper climb gradient) than a SID, which is more "situational" and provides a specific direction in order to enter the en-route structure. Take, for example, the takeoff minimums for the La Guardia Airport, page L16. It states, for Runway 13, "400-2¼ or std. w/min. climb of 280' per NM to 500". On the other hand, this SID, also for Runway 13, clearly states as takeoff minimums "Standard with minimum climb of 563' per NM to 710, then ATC climb of 615' per NM to 2500, then ATC climb of 605' per NM to 4000, then ATC climb of 367' per NM to 5000". My question is, why does this SID require steeper climb gradient than the ones listed in Takeoff Minimums for La Guardia Airport?