I have to say that the system lends itselve more toward dungeons than above ground wilderness adventures. That is to say, it is biased toward monsters in rooms within some kind of complex that must be traversed in some fasion toward some end goal. Whether that be a dungeon, a temple, a keep, or anything else along those lines, that is what the main game was designed with in mind.
I say this becuase of the way the CR system is set up, how movement is done, the fact that there arn't rules for large scale battles, the rules for traps, various monsterous races, many spells that assume close formation fighting, and many things I found to be implied while reading through the books. That is not to say that you can't have a great non-dungeon delving campaign. I run many city based adventures and wildnerness adventures and have my entire DM career. Just, dungeoneering was the main focus in balancing and desiging the D&D game.