Blizzard announced recently that they are increasing the power of gear that comes from the newest raid zone. It used to be that the gear from the old zone was 655 or 670 item level (from Normal or Heroic respectively) and the new zone was 665 / 680. Now the numbers will be 655/670 for the old and 670/685 for the new. The adjustment is a relatively small one but it makes it clear that they are very carefully trying to figure out exactly how to dole out rewards. What is interesting to me is trying to figure out exactly what their goals are in doing this.
Upping 665 gear to 670 means that the old zone has been rendered much less meaningful in terms of farming up gear. Any group that can easily clear it on Heroic probably has most of their gear 670 anyway, so they are doing the new fights and not worrying as much about farming. Anyone who can't get Heroic mode down easily in the old zone is probably moving right over to doing the new one on Normal because it is slightly easier to get the same quality of loot.
The thing is people are hugely motivated by those numbers. If the new zone was harder but had the same item levels the great majority of the people wouldn't try it. They would just stay in their comfort zone. Blizzard wants people to keep on trying new things because that is fun and fun retains players, but they don't want the old zone to empty out in an instant either. Blizzard is trying to create just enough incentive for people to try new things by having the rewards be slightly easier to get, but that is a tricky thing because people are already used to the old fights so they are naturally going to be easier to execute than new things that need to be practised.
My sense is that originally the Normal mode new fights were a touch easier than the Heroic fights of the old dungeon and consequently awarded slightly lower level gear. However, practice makes such a difference that people weren't terribly interested in putting in the effort to learn new things when the rewards weren't ratcheted up enough. This is particularly true because guilds definitely get to a point where they can farm the old content on Heroic and the new content on Normal and then realize that all those 665 drops are invalidated by 670 drops and the new dungeon suddenly seems pretty worthless until you can actually beat it on Heroic.
It really comes down to how people look at the content. If the new stuff was only slightly more difficult but awarded slightly better gear people would go there. That is, if Normal raiders went from 655 to 660 it would have worked. But since the new zone was closer in item level to the old Heroic it got balanced and compared to that and it suffered by that comparison.
Given that Blizzard really didn't want to nerf the gear, nor to nerf the content itself, they really had no choice but to push up the item levels for rewards. I think this new set of numbers will do what they want - provide incentive to move on to the new zone without totally invalidating the last one, at least not right away.