I don't think it's explicit about the fiction at all. It's telling you that the first priority is to set an "appropriate DC"... it then goes on to give an unclear example of what exactly is appropriate at that level/DC. IMO that's one of the problems with 4e's DC's... it tells you... "Hey set an appropriate DC then construct some appropriate fiction... but it doesn't give you a good basis to design said fiction. In the example above you cited is it saying majority of your doors should be barred? That the PC's should never run into wooden doors at that level or that iron doors are too hard?
Because appropriate DCs are what work. Remember, 'appropriate' doesn't mean 'a specific DC'. In the iron door example it says "unless you want it to be hard", so maybe the iron door IS appropriate, IF you want a hard to open door. The normal assumption is that you want Medium DCs. This is not vague in the full context of the section, as a few pages below are listed the DCs for various doors, with the iron door at DC 26, the wooden door at 16, barred door at 20, and there are some others too. So, if you look at the DC chart level 10 medium DC is 18, which means a wooden door is easy-ish, and an iron door is fairly difficult. Barred doors will be a good element to use for a door that is challenging but should fall to the PCs attempts without a lot of extra effort. You should of course note that these are 'typical' DCs and are called out as examples. You don't have to put barred doors in all your dungeons just to satisfy a DC, you can simply say "the wooden doors here are on the stout side, made of dwarvish mountain oak, DC 18." But note, now you've done exactly what people seem to be resisting admitting 4e does, make the world's fiction and mechanics consistent.
I also think it's combination of objective and scaling DC's causes a certain incoherency in the game when it comes to challenges... as illustrated by the difference between a wooden door and the Cave Slime I mention below. One's DC is objective and the other one's is level appropriately based...
The terrain text illustrates exactly what some of the people in here are talking about. If you look under Cave Slime, it states...
"This thin blue slime is harmless but extremely slick. A creature that enters a square filled with cave slime must succeed at an Acrobatics check or fall prone. Use the difficulty Class by Level table (page 42) to set a DC that's appropriate to the character's level."
The rules are specifically stating that this slime scales with the PC's levels... so even though their level and bonuses increase, their chance to not slip stays the same. This is exactly what I and some of the other posters are talking about in this thread... and this isn't the only one written like this.
But again, there's no indication that AN INDIVIDUAL PATCH OF CAVE SLIME has a different DC for different characters. Just that in a level 20 area its level 20 cave slime, and in a level 5 area its level 5 cave slime. Presumably you'd describe it that way (IE this cave slime looks particularly thick and slippery). Probably in the level 20 area you don't even bother to describe the bits that are thin and not too slippery (IE level 5) as nobody even cares at that point, all the PCs will auto-pass a level 5 Medium DC. You are of course again free to decide what is appropriate, maybe you want level 20 cave slime so the PCs get shot down a slope and can't catch themselves at level 5. Go for it!
Again I am asking where is this stated. IMO, and I've brought this up before in other discussions, 4e confuses the matter because it is a mixture of objective DC's which are tied tightly to the fiction and scaling DC's that aren't. And, as seen in the case of some of the terrain the fiction is not always changed to match a changing in the DC's.
Well, presumably there simply isn't enough page space in the DMG to make up 5 kinds of cave slime that have different DCs. The whole section is examples, sort of 'dungeon clip art' for the DM to borrow. Chances are you use Cave Slime a few times within a specific level range and then 10 levels later in some totally different environment you can have 'Elemental Cave Slime' or something. In fact later DM resource books all have sections detailing specific terrains that are useful in those places.
As for 'where it is stated' that encounters are level-appropriate? It is assumed throughout the whole system. Explicitly the Adventure construction chapter of the DMG has a chart on page 104, part of a whole section on that page, which directly addresses the range and mix of encounters in an adventure.
To address your other statement about level appropriateness and encounters... you listed 3 types of encounters... combat, skill challenge and puzzle. You state that combat and skill challenge are supposed to be built around appropriate level DC's, so that leaves... puzzles? How do you even make puzzles level appropriate? Of course they give rules for puzzles as SC's in which case you would design it as level appropriate.
Puzzles are described as player tests, and then they describe how you COULD use checks as part of the puzzle, if you want. Its a way of describing for the DM the process of giving the players a challenge instead of the characters. Its rather 'retro' for 4e I guess, but its a time-honored aspect of D&D, so they describe it. I didn't talk about them because there's really not much to say. They don't have any math (or else they are just SCs).
Yes but this has nothing to do with level appropriate challenges and everything to do with capability. In other words it is not the fiction around difficulty that is changing... it is the DM judging that the capability to address the challenge in that way is not there.
My point is that the world doesn't just consist of a huge list of the Medium DC. Clearly in any city street there are a billion things a PC could theoretically do, but 99.999% of them are impossible for your average low level PC. In other words they have DCs that would require epic or even godlike bonuses to pass. Some may be just ridiculously hard (IE you might be able to steal the gem off the statue that is in plain sight in the busy market square guarded by 10 guards if you pass a DC31 Stealth check. This is BARELY possible for a super optimized level 1 Rogue, go for it!).
None of these DCs scale, they won't be harder or easier at different levels, they represent objective reality. The DC chart just tells you which characters at what levels you can expect to pass them.
This is my point though... not only is it not discussed... it's the opposite of everything the DMG 1 puts forth. In other words having level appropriate DC's is stressed throughout encounter design.
Yes, because encounter design talks about combat encounters of appropriate level, which are assumed to be ones that the PCs can win most of the time, but will find challenging. There isn't a lot that need be said about trivial encounters that you just win, or ones that if you attempt them you just die. They hardly need be designed at all! And as far as SCs go, again, it makes no sense to design ones that the PCs can't pass. The players should be saying "gosh, we're first level, we can't take on the Vampire Lord, lets not go try to intimidate him" instead maybe they go look for a holy sword.
Obviously its possible for players to just not get the idea, or want to, go and do things that are basically suicidally hard. Maybe they can find a way to succeed, nothing in 4e suggests that adventuring 'off level' is bad or impossible. It just doesn't get a lot of airplay because presumably you don't need guidelines for making things too hard.
