Just want to throw my hat in with the group that observes that 4e's engine is built off of subjective, scaling environmental DCs that are predicated upon genre/trope challenges for level/tier equivalent characters. I've been running 4e since its inception with merely a flashcard with the current level's DCs, damage expressions, minion damage, average and + HPs, average ACs and NADs, + vs AC and + vs NAD, and Skill Challenge info. I've got a few flashcards for monster themes (for all of the roles) to add to a basic chassis. Of course I have the laptop with the Compendium up when I need it.
Both the DMG1 and DMG 2 work off of this premise. There are a few sections with a tacit nod to a few objective metrics (Jump DCs for combat and manipulating doors specifically) for folks who want them. But just like 13th Age, Heinsoo's D&D was definitely predicated upon environmental DCs that scale with PCs through the levels/tiers and require the GM to scale the fiction of the adversity with the PCs. Conflict Resolution systems go all pear-shaped without predictable, bounded math.
At this time I'm going to pull out some quotes so we can get off this subject and back onto the original subject of the thread (all used under fair use laws):
DMG1 page 42:
"Cast the Action as a Check: If a character tries an action that might fail, use a check to resolve it. To do that, you need to know what kind of check it is and what the DC is.
Attacks: If the action is essentially an attack, use an attack roll. It might involve a weapon and target AC, or it might just be a Strength or Dexterity check against any defense.
For an attack, use the appropriate defense of the target. Use an opposed check for anything that involves a contest between two creatures."
Note that you use the AC or defense of the target creature as the DC.
"Other Checks: If the action is related to a skill (Acrobatics and Athletics cover a lot of the stunts characters try in combat), use that check. If it is not an obvious skill or attack roll, use an ability check.
Consult the Difficulty Class and Damage by Level table below, and set the DC according to whether you think the task should be easy, hard, or somewhere in between. A quick rule of thumb is to start with a DC of 10 (easy), 15 (moderate), or 20 (hard) and add one-half the character’s level."
Here we see that they say use an easy, hard, or somewhere in between check based on the characters level. So if they are high level and improvising with a low level obstacle, then they would obviously cast it as an easy check that would be really unlucky to fail. So again it is based on the tasks difficulty compared to the character, not the characters level compared to a chart.
On page 61 of the DMG1 it talks about terrain and uses the phrase "the DC of the terrain" over and over. So the level of the terrain determines the DC, not the characters level.
This here is the clincher on page 64 of the DMG1:
"Terrain and Skill Checks or Ability Checks: When terrain requires a skill check or ability check, use the Difficulty Class by Level table (page 42) to set a DC that’s appropriate to the characters’ level.
Some of the examples below show DCs for breaking down doors or opening locks, and also show the level at which a character should be able to break down the door with a Strength check of moderate difficulty. Thus, that level is a good rule of thumb for dungeon design. Don’t put an iron door in a dungeon designed for 10th-level characters unless you intend it to be difficult for them to break through."
Which shows that the DC is a property of the level of the object and not a product of the level of the characters.
They wanted you to use the proper level of objects and challenges so that the players don't think you are being sadistic and to that end they gave you a chart with a range of DC's to tell you what a certain level of characters should find easy, normal, or difficult. Not the other way around.
Essentials took all of that explanation out and instead just said look on the chart and choose a DC by the characters level that is easy, normal, or difficult...