I slept on 4th edition almost entirely. There's a 5e round-table discussion from last year hosted by Koebel, in which not only is the DMG 2 described as much better -- which is something I've heard before -- but also there are things in it that WOTC could never have known when writing the first DMG. Since it's a conversation about 5e, the discussion never returns to this specifically.
Without expecting you to be able to part that pink mane and make psionic contact with his mind, what might some of those things he's referring to be?
I've seen the differences between DMGs in 4e described here on this site as somewhat boiling down to things like an emphasis on "Group Story Telling; Advanced Encounters; Skill challenges; Customizing Monsters; Adventures; Paragon Campaigns..."
None of those things strike me as a "could never have known" situation, and I expect they're probably too big and broad to be what was alluded to in that clip, in that I'm guessing the things in the DMG 2 that he's referring to were more on the order of extremely smaller snippets of advice or wisdom.
So what are some of the smaller, "Oh yeah, it turns out 4e games run like such and such, and so a good idea would be this and that"-level pieces that come to mind?
Or am I wrong there, and actually Group Story Telling is the sort of topic WOTC could not have known how to write about when designing the first DMG in the context of 4e?