My apologies for a recent flippant remark saying that there were only 3 people out there actually reading the lore. That was an unjust exaggeration. But I'm afraid I'm going to cause further unhappiness to the lore fans with this post. The thing is that both Keen and /random are discussing how sad it is that WAR only has 2 realms, not 3. Quote: "Rock-Paper-Scissors is a lot more fun than Rock-Paper, ya know?" That made me think *why* Mythic chose to go for just two realms. And the answer is definitely the lore.
Whether it is Tolkien, Star Wars, or the Warhammer lore, most epic war stories are good vs. evil. In real history "good" and "evil" aren't so clearly defined, but 3-way wars are still extremely rare. 3-way fights are a lot more common in video games which don't start out with an existing license. Dark Age of Camelot or Starcraft didn't have pre-existing lore which would prevent them from having 3 warring parties.
If you have "good" and "evil" fighting each other, what third party could you add to that? "Neutral" doesn't seem to be a good choice, because why would they fight the two others instead of just staying out of it? Furthermore the interest of 3 realms is that any two can gang up against the third. Can you see good and evil allying themselves against those wicked neutral guys? It is a lot harder to come up with a good story of why there are three realms, all equally strong, with any possible combination of 2 against 1 working as well as free-for-all combat of everyone against everyone.
So as long as MMORPGs use lore from other sources, we won't be seeing many 3-way wars anytime soon. A third party in Warhammer Online: Age of Reckoning simply wouldn't work well from the lore point of view, even if it would be an improvement from the gameplay point of view.