If you've played World of Warcraft for any length of time, you've probably heard the refrain that game balance is most important at endgame. Whatever endgame happens to be at that time (level 60, originally; level 85 in Cataclysm), the idea is that a little weirdness in talents, abilities, survivability or damage output as you level up isn't as important as making sure things are working properly at maximum level. While it may still be true, recent forum posts indicate that the leveling game and even the current, soon-to-be-moribund maximum level of 80 are seeing more balancing passes now than one might expect.
I wouldn't call it a change of direction, as Blizzard has never said it doesn't adjust lower levels, and clearly a great deal of Cataclysm's focus has been on content for leveling players, but it does show a willingness to make changes in the face of oddities of design. (The original poster notes things like rogues soloing Scarlet Monastery while level-appropriate.) With more people than ever leveling through battlegrounds or the dungeon finder, the lower-level experience is actually pretty compelling and important. It's good to see some design time aimed at fixing its problems.