Shaun,
They really are different in the way they work - the situation you described ilustrates the effect of this.
Once micro-splitters have done their job (pre-conditioning), multiple passes will remove soil whilst it is in the pile.
The extraction detergent is designed to rapidly capture soil at the spray/extract stage - once it is removed from the carpet it cannot continue to do this.
Before the advent of micro-splitters I often used a fresh-water rinse, but the soil had been treated by pre-conditioners designed for that purpose.
John.