Hello all,
Realism and flavor are our top concerns. Ideally and realistically the counterstrike and damage barriers are supposed to be simultaneous.
During development we had to make some tough choices as to when to sacrifice realism in order to keep the game simpler and easier, and this was one of them. We decided to break up all events and actions into steps, and try to keep things from happening simultaneously. For example, with Counterstrike and Damage Barrier, it creates weird anomalies when they are simultaneous. A simple example is with Vampiric trait - when does the creature heal back his damage if he dies simultaneously from a Damage Barrier? It keeps the game system cleaner, and paves the way for interesting abilities later that function better where events are sequential.
Once we decided it was going to be best to go with sequential events, we had to decide where to place the damage barrier step. Initially it was at the beginning of the attack "you have to step through the barrier to reach your target". But, that made damage barriers even more powerful (and they are already extremely powerful) so we moved it to after the attack occurs.
On counterstrike, although the original intention was to be simultaneous, we felt it was not too much of a stretch to say that the attacker strikes first, and the counterstrike is a reaction to that attack, occurring a split second later.
However, there are exceptions: We have a coming High Elf guard with a long halberd that can strike first when guarding. His text reads, "When guarding, Temple High Guard gains Melee +2 and may counterstrike first (the Counterstrike Step is moved to just after the Declare Attack Step)."
Hope this helps!