Frankly, I think the DMG 2 is the book the DMG was supposed to be in the first place. I think the DMG was supposed to be a book on 'how to be a dungeon master?' not 'use these massive lists of traps, magic items and prestige classes and do what you want with them' book.
Sure, the DMG has a few blurbs on what different kinds of games consist of, a chapter on world building (which doesn't help a damn on actually building a campaign world), a large chapter on dungeons (and a random dungeon creation chart), the experience point chart, rules on wilderness situations (something actually useful), and rewards. I am probably overlooking a small few items of note, but the DMG is not a book that teaches somebody how to be a dungeon master.
The description of the DMG 2 sounds, to me, to be that book they need for helping DM's become actual DM's.