It certainly looks like Blizzard is attempting to allieviate confusion among players regarding various systems in World of Warcraft. First Bornakk gave players a lesson in looting items with the Dungeon Finder, and now the blue poster is shedding some light on the balancing act that comes into play between factions in Wintergrasp:
"When one faction defends more than the other, the system will give advantages like the ability to use catapults or siege tanks faster to the faction that is on the offensive. On realms where one faction is often able to defend the fortress and the other faction rarely defends, the system tries to help this balance by providing bonuses to the faction that rarely succeeds at defending."
Bornakk couldn't provide more exact details since they don't want players to abuse the mechanics, but it's an interesting glimpse into how Blizzard is trying to keep the battle balanced. What's Wintergrasp like on your server?