The reduced experience in Alterac Valley is due to the fact that Battleground experience is based off of the level of the Battleground. Characters level 70-79 are no longer getting experience based on level 80 characters. As a result of this, we are now able to do an across-the-board increase to experience gains from all Battlegrounds in order to make sure that no Battleground feels too unrewarding in terms of experience. We have also made it so the experience bonus from heirloom items works properly in Battlegrounds.