In my last post, both Lizard and and Irda Ranger (sorry, but your EN World handle is how I think of you!) brought up some points I've wanted to talk about for a while now.
The 4e DMG is not a book about world building. It was never intended to be one, and it consciously avoids the topic.
The reasoning behind this move is quite simple. The DMG is meant to be the first step for a 4e DM, and in particular a *new* DM. One of the big advantages D&D has over other games, particularly computer games, is that someone gets to be the DM. A lot of games nowadays allow you to be a dwarf fighter, bashing orcs over the head and looting dungeons, but D&D (and by extension all RPGs) is the only game that lets you control the orcs, place loot in the dungeon, and draw the dungeon map.
We avoided focusing on world building because we wanted to avoid giving DMs the impression that they had to do lots and lots of work to run a game. Now, you can put a lot of effort into your game, and IME more effort means a better game, but we didn't want to daunt a beginner. A new DM can run a perfectly fine game by stringing together some encounters and focusing on the tactical, rather than strategic, end of the game.
As an aside, that's also why there's a sample starting area and a rather simple beginning scenario. Now, it's tricky, because the DMG has to serve both existing D&D fans coming in from earlier editions, and new players, but the idea is that established DMs already have info on worldbuilding from other DMGs and other resources.
Now, on to the second topic and the inspiration for this post's title: exploration. There is woefully little exploration in many of the current crop of 4e adventures. I don't think it's by a design that sees exploration, or the stuff between encounters, as bad. The seed of that design mode has good intentions - give DMs as much for their buck as possible, with bang equating with encounters (usually fights) rather than descriptions and background info.
I can see how those two trends dovetail to generate some of the criticism of 4e. The two are separate, but both do have reasons (though you can debate the legitimacy of those reasons) behind them.