In GW2 you are no longer frozen in place when you attack from range. But the mobs doesn't take advantage of that. They just stand still as long as you are "in range" of their attack.
There are no reasons for them not to move. Even a sample "Move left for 2 seconds. Move right for 2 seconds." movement while in combat will help them avoid a lot of hits.
On that note, there are zero reasons for ranged mobs to stand in AoEs. They should dodge out of there asap.