This could not be further from the truth as I will show.
I call myself a Young Maelstrom Creationism Advocate (YMCA), I am an expert on WoW lore, and I believe that the Maelstrom was created by Deathwing around 1 or 2 months ago in WoW's timeline, when the Cataclysm began. Before that it did not exist in Warcraft lore. But when Deathwing decided to break out of Deepholm (which is literally at the center of Azeroth contray to what Elemental Plane theorists say, it's not in the Twisting Nether, it is merely cloaked by a magical layer beneath Azeroth's crust as can be seen in Deepholm's ceiling) he created this rift by shattering the World Pillar into 3 fragments. Why 3? 3 is the number of perfection. If it had been more, Azeroth may have all crumbled.
When the World Pillar was damaged, all the ground above held by this Magical Pillar crumbled and so the Maelstrom was formed. Deathwing then used powerful incantations to break thru the infinite magical substance between Azeroth's crust and Deepholm.
Aggra clearly states that the Maelstrom is a rift between Deepholm and Azeroth and that it threatens to destroy Azeroth. If it had been 10000 years old as War of the Ancients historians say, it would have destroyed Azeroth ages ago:
"We're at the center of the Maelstrom, the rift between Deepholm and our world. Watch, as it threatens to tear our world apart."
"Let us hope Thrall and the others can contain it while you're inside." - Aggra
So if it needs "containment" from the most powerful Shaman, why has it existed for 10000 years without harming Azeroth or the islands near it? The answer is quite simple, it is recently formed, created by an intelligence and as a deliberate act (by Deathwing) not by some random explosion. It is a known fact that the Well of Eternity never exploded, it still exists beneath the World Tree in Kalimdor.
Common War of the Ancientists' objections:
1. It's talked about in Warcraft 3. - "Maelstrom" is a broader term that can mean many other things, for example it can mean storm, there are also other smaller maelstroms in Azeroth.
2. Why doesn't the water fall into Deepholm, it should be flooded - Water cannot pass thru the magical substances between Azeroth and Deepholm, only living beings attuned (and their armors) can. Water simply cannot, it just keeps spinning.
3. What happened to 80% of the landmass? It is likely that the landmass disappeared NOT from the Well exploding, but by some evil Burning Legion magic in the final battle or a Highbourne spell gone wrong.
4. Why was there a Maelstrom on vanilla WoW's map then? Simple, Blizzard had it planned. Vanilla WoW is alpha Cataclysm, notice how the bosses are Ragnaros/Nefarian and there are Twilight cultists everywhere, especially in Silithus.