Out of 5 machines I've used at different apartments, none had a separate pre-wash dispenser. And I've saved manual for my current one, it says nothing about adding detergent additionally to the dishes. And all of them washed just fine with powder, without any additional mumbo-jumbo.

i have dishwasher that is loaded with cartridge that has 400g of powder. ideal scenario for dispensing detergent at will. yet, never mind what cycle I am using, it dispensed only during main wash cycle.

i also had in past machines from 5 different manufacturers. none of them had mechanisms that facilitate 2 releases or pre-wash compartments