I maybe wrong. But i think compiler ommit System.Diagnostics.Debug for release builds.
But you gus replaced all Debug.Trace with CCLog. And all debug information (messages and other info) exist in release builds.
Its not shown anywhere, its not big cost of size or performance, but its still exist in release builds.
Forum topic: http://www.cocos2d-x.org/boards/17/topics/11690