When it comes to scaling of skills over levels, is there any good reason to do so the way 3E/4E does, other than:
1. Psychological - reinforce with bigger numbers that things that were tough at 1st level are easy at 10th.
2. Handling time - scaling is built into the system so that you have a d20+mod roll at any given level.
Reason I ask is that one potential way to make scaling more flexibile is to explicitly not embed the scaling factor. For example, say that the scaling factor is 1:1 with level. Characters have a level. Things to overcome worth XP have a level (e.g. traps, hazards, skill challenges, etc.) You get a postive or negative mod based on these levels.
So climbing a rough wall is DC 15 (whatever that entails). Against this, any character can put their athletic skill, climbing gear, etc--d20 + mod, right off the sheet. A 2nd level character encounters a 5th level rough castle wall (whatever else that entails). He gets a -3 to his roll. Later, he comes back as a 6th level character and climbs the same wall. He gets a +1 to his roll. Conceptually, no different than what 4E does now.
However, say that 2nd level character gets over the 5th level rough castle wall. Later, he comes to the inner keep, which is a 7th level rough castle wall. Nothing has changed on his built-in mods. The DC is still 15. However, now he gets a -5 to his roll. This wall is just a bit worse (taller, smoother, whatever). Very similar to now.
The differences might be in the perception of the rules by the players, and ease of remembing the difficulties. Because now the rules are subtlely reinforcing the intent of 4E, which is that only things tough enough to matter and having consequences for failure should be even getting rolls.
Likewise, if the novice DM goes to design his castle, he is making an explicit choice: There is nothing special about the rough outer walls? Just use the default DC 15, assume level 1, and characters will increasingly breeze through as their level increases. However, if the DM wants the wall to be a challenge, then he is giving it a level somewhere around the characters' level, and is thus confronted with explaining why this wall is tougher than the default.
There might be some XP mapping potential there to build upon the already excellent 4E budget rules, but the main point is that even minor changes to the presentation of the same mathematical rules can have an effect. (I know 4E is 1/2 level bonus, not full. But same basic ideas are in place.) Also, if the scaling factor is explicit this way, each table can more easily house rule it out, change it, or make the default fit the implied world.
