There's a really big difference. The Aspects were created by the Titans, and charged with watching over the various aspects of the world. The Ancients, on the other hand, were spawned by Azeroth itself. While the exact date of the Ancient's existence isn't really known, we've been told in the novel Wolfheart that the Ancients were actually born of Azeroth itself, not created by the Titans as part of their grand organizational scheme. Demigods, loa, whatever you want to buy wow gold and call them -- they were all created by the planet, not by the Titans.
Now that's interesting, particularly given the nature of the world as we know it. We know that the Ancients and the Aspects worked together -- in one case, we know an Aspect actually fell in love with an Ancient. Ysera loved Malorne, and although Cenarius was the son of Malorne and Elune, Ysera treated him as if he were her own son, odd as that may sound. But the connection between Ysera and Malorne makes perfect sense, in the same way that Kalecgos and Anveena's relationship makes sense -- Ysera was charged with watching over and protecting nature, and Malorne was pretty much nature in a corporeal form, much as Anveena was magic in a corporeal form.
For some reason, the planet Azeroth decided to spawn these demigods that watch over the world. It may have been for the purpose of protection, or a defense mechanism. But if Azeroth decided to spawn these creations, why did the Titans deem it necessary to put the Aspects in place to sell wow accounts and do pretty much the same thing? Why would you need a fabricated security system, if the house already came with one, pre-installed?