World of Warcraft has a dizzying mix of technology levels. There are rocketships and iron swords; motorized roadways and stone monoliths. All of these mixed messages seem to indicate that, all at once, WoW is populated by high and low tech societies. Why is this?
The Magic Factor
It seems that WoW's magic may have something to do with this. Everything we've seen of Goblin or Gnomish engineering implies that it's heavily quirky, specialized and often dangerous. Is it possible that the magical nature of Azeroth simply doesn't let technology progress smoothly? Perhaps technology is held back from reaching its otherwise likely end-point by magic.
In fact, this is made to seem all the more likely for the fact that Goblins in Outland have managed to build a mostly functional rocket ship in a short time while here, on Azeroth, they've been toiling away for centuries only to come up with unreliable and dangerous teleportation and an electric shock device for reviving people whose hearts have stopped.
The only other conclusion would be that there's an active decision which has been made to hold back the growth of technology and I don't think it's very likely that the Gnomes and Goblins have agreed on that.