This is what DM David was discussing. A standard wall is always the same DC, but the kinds of walls the PCs encounter scale up with them (via increased fluff to their descriptions). The mechanical effect is you start at a baseline percentage chance of success and only creep a little bit over twenty levels when taking on level-appropriate challenges.With regard to the level DCs, my understanding is that it’s still environmentally based. So that wall that was a DC 15 to climb, will always be DC 15 to climb. Another wall ( an abyssal wall of spikes, flames and grease) would have a higher DC because you need to be higher level to even survive that environment and it would be a lot harder.
Saying this is environmentally based is just cover for the treadmill. Sometimes the devs slip. There was a blog post a few months back that described a navigational challenge through a maze. They advise scaling the to the level of the PCs. No fluff!