For the airline I work for, slides are NOT ARMED until the aircraft is sealed (boarding finished, doors closed).
It is not safe practice to remove rear steps (or obviously front) BEFORE fuelling is finshed.
So to conclude there is no need to arm the doors on the ground because the steps are still there! Simple really.
The FCA incident has been traced down to an icing fault. The door WAS disarmed but the 'mechanism' that arms/disarms the door was frozen in place hence the slide dropped out upon opening the door. Gladly, the catering truck was there to catch it.
