There is a difference, albeit of academic nature... TOD is up to screen height, where TOR is to the point where the wheels leave the ground.
The segments are a logical way of describing the various phases that most aircraft go through during a departure. Gear up and clean up are such events that define the various phases and each event will affect performance in its own way. Therefore, why not let these events define the segments so that also the performance requirements may follow? I think its logical at least.