Is James Cameron Pushing His Luck Doing Avatars 2 and 3?

Deadline broke the news this morning that James Cameron is already writing the sequel and three-quel to Avatar, and will shoot them back-to-back, aiming for theatrical releases in Decembers 2014 and 2015. Sure, the first one was a game-changing megasuccess, but the precedents for two-at-once sequels to a smash hit are not heartening (c.f. The Matrix Reloaded/Revolutions and Back to the Future Part II/III). Is Cameron making a mistake going for the three-peat? Or will the Avatar trilogy be the Lord of the Rings of the 2010s?