^Not sure what the correlation there is. The black Nick Fury is not a creation of the movies, it's from the "Ultimate" line of comics, from which the movies have borrowed very heavily, so it does come from the source material. Besides, there is really nothing intinsic about the modern Nick Fury that states he must be played by a white man. If they were doing the WW2 "Sgt. Fury" version of character, then race might be an issue, but as long as the character is well-written and portrayed, I wouldn't care what race of actor portrayed him in the modern context. Hell, one of the only good parts of the Daredevil
movie was casting Michael Clarke Duncan as Wilson Fisk.
The Last Airbender
, on the other hand is specifically portrayed as taking place in a culture with asian influences, asian names, and asian people. So the casting of caucasians in the starring roles is a bit more glaring in that instance, and was basically just pulled out of M. Night Shalayman's ass without any regard to the source material.