Level 80 AV Bracket Added Early, But Will Stay
UPDATE: Crygil has explained that the reduced experience in AV is because "characters level 70-79 are no longer getting experience based on level 80 characters." As a result, Blizzard is going to increase exp gains from all battlegrounds. Also, the exp bonus from heirloom items now works properly in BGs.
Bornakk has clarified why level 80s now have their own separate bracket in Alterac Valley in patch 3.2.2, and it looks like the change was made by accident. The World of Warcraft development team actually planned to switch around the brackets in 3.3, but the update was "accidently applied" to 3.2.2.
Since the developers eventually intended to make the switch, Bornakk said they've decided to keep the brackets set up like this "so that players who are leveling play together and players who are at the level cap play together." Bornakk also said the levels of the bosses in the brackets below level 80 will be reduced to compensate for the change.