I read somewhere that blizzard's MO is to try both extremes, then meet halfway. At first the leveling curve was too easy, now it's harder. I honestly think that they are just trying to manipulate certain aspects of the beta. I imatine that at first they might have wanted players to move up fast, so spread them out a bit, and now that they are spread they want it to stay that way.

Its all beta, so its likely to change.