According to various accounts, the Titans have had their hands on almost every inhabitable world in the universe. Certainly Algalon had to keep an eye on more than one planet in his impossibly-long life -- he says as much when we stop him from sending the signal that would re-originate our world. This fact alone is enough to indicate that in the Warcraft universe, worlds aren't quite as unique as we'd expect them to be. If the Titans had a hand in their ordering, they're likely going to have at least some similarities.
But it doesn't mean that every world we come across is going to be just like Azeroth. We've been presented with the idea, time and time again, that Azeroth is unique in the universe. It's special. There's something about it that sets it apart from every other world. And yet, when you hold Azeroth and Draenor next to each other and take a good long look at what they are, you can see the bare bones of what was once upon a time, a blueprint shared between the two. Unfortunately, the comparison raises more questions that it seems to answer -- but those questions are pretty important.
Today's Know Your Lore is a Tinfoil Hat edition. The following contains speculation based on known material. These speculations are merely theories and shouldn't be taken as fact or official lore.