The faction hording of Wintergrasp happens particularly often on unbalanced realms. Because the faction imbalance can be so extreme in some cases, the smaller population faction has virtually no chance at winning back the Wintergrasp fortress and obtaining the heirlooms and PvP items, nor any chance at accessing the VoA bosses. This can cause frustration on the part of players in the smaller faction.
In this mechanic, which we presume is live, Wintergrasp zone mechanics will make it easier for the offense to gain access to siege vehicles if the opposing faction holds Wintergrasp more often. Blizzard is not specifying how long the opposing faction must defend Wintergrasp for the the offense to receive these significant buffs, but one can assume there is some sort of threshold.
The full Blizzard statement after the break.
We wanted to address some of the confusion we often see regarding the Battle for Wintergrasp. We will not provide exact details on how the system works to try and avoid abuse of the mechanics, but there is a system in place that can change how the battle plays out.
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.