1) The +2 to damage if your mount doesn't move, is this implying that your mount is also attacking your opponent? I ask because I would think that moving while fighting should increase the damage in some way, if going fast enough, because you have more force that you can apply to your swing with the horse's movement.
I was curious on that count, too. That bonus doesn't seem to make an awful amount of sense.
I suspect that the “+2 damage” follows the same rational as the use of an Off-hand weapon. In any case it isn’t an intuitive solution, nor is an easy one to describe in play.
It would be nice if one of the developers/designers come here and shed some light on the issue.
On the other hand, the rules for mounted combat (the rider using its animal handling value as bonus dice to fighting), and the advanced rules for TRAMPLE are very intuitive and easy to explain.
2) Is your Armor Penalty or Encumbrance penalty negated or reduced when fighting on horseback? I think it should, as your horse is helping bear your weight.
When you are fighting on horseback, you use the mounts movement, thus effectively negating bulk penalties to movement.
I think that the Armour Penalty to Combat Defence and Agility is NOT negated, which I believe that is realistic and makes perfect sense.