Did you know that different zones are at different points of time?
For the most straight-forward example, loot at Tempest Keep and Magister's Terrace. kael'thas is in both, but it is not at the same time. Magister's Terrace, in fact all of the Isle of Quel'danas, exist after the events in Netherstorm.
Other examples include any quest chains which move across zones. The earlier quests are at an earlier time, and so their zones are as well.
Escort the Taunka from Taunka'le village and you've moved them to a slightly later time in which they are refugees and are moving both to the Horde base in Dragonblight and even further east to Grizzly Hills.
This is a side effect of a combination of static universe but advancing story. Yes, the story does advance. We are not mere observers learning more as we go along, we are changing the world.
Why does this matter? It can cause some weird problems when Blizzard updates content.
For example, the Plaguelands used to exist at a time before or during the first assault on Naxxramas. As far as the NPCs in Light's Hope Chapel are concerned, they still are. However Naxxramas is gone, which means that the areas of the zone where it was once visible are not in a later time, a time after it moved. That means that within the zone there is a time difference of years: the time of when the citadel arrived and when it left. Except Light's Hope must be in a later time, since there was the DK starting event; that should have pushed it ahead. Yet we appear to simultaneously see both the eastern coast destroyed and the Scarlet Crusade in the chapel preparing for a suicidal assault on a necropolis which is no longer there. What time is it?
How will the recreation of Azeroth affect this between-zone time travel? I have no idea.
In other Plaguelands business,
One of my guildies recently started a blog. It's here. If you like my posts, then you might like the most recent post about the plaguelands and other WoWness. I suspect because it's influenced by a conversation we had a few days ago. It's a different expression of the balance of world and game.