The game in general is continually in a process of dumbing down.
It is actually a smart move on Blizzard's part.
The whole 99.99% of the player base gets to experience 99.99% of the content, during the current expansion.

In the newbie zones, the previously hostile starting mobs, such as the demons in the cave near Org or the Defias guys across the river near the SW newbie area, are all non-aggro.

My druids are mid way through 68th now (have done Hellfire, Zangarmash, Terrokar and have barely touched Nagrand), the one with two pieces of (experience boosting) heirloom gear is 64% through level 71... and has never been to Northrend (or BeM, Netherstorm, SMV). Given how easy BC is, and how dead it is (no competition for mobs), and how crappy a lot of the Northrend collections are... staying for a while might be a good idea. A lot of the quests require far fewer mobs too; the Nessingwary quests are 12 mobs of each type instead of 30.