I think that lower levels stuff going faster is quite a good point really, hard lower level stuff is great when the game has just been launched and there is a ton of people playing in the lower tier of the game, but Wow is old and there isn't that much people down there any more.
The thing that ****es me off, and keep in mind I don't play Wow any more (Stopped just before Wrath of the Lich King) , is that they made the max level dungeons so unbelievably trivially easy. At least its my good mate telling me this, with which I played Wow before I stopped, he's one of the best stuffed druid on his server. If there's not even any challenge at max level there is no point in playing imo. What I found nice in TBC was that the high end dungeons were that, high end..., only a small portion of the server could go there without dying repeatedly.