Should characters have the tools to take on wildly non-level appropriate challenges, though? What is a level appropriate DC for a 10th level character. Why is that a level-appropriate DC for a 10th level character? Under the current skill system, that question cannot be answered for the general case, it can only be answered for the particular party that is encountering the challenge.
Please stop concentrating on the specific skill examples I'm using - I think I'm going to start using opposed skills from now on; as opponent skill levels should scale with Encounter Level (as should envirnmental DCs in many non-opposed skill encounters according to game design).
Let take a look at a different "gateway" encounter: The PCs have to get a particular item from an NPC - this is a an encounter with an EL equal to the party's APL, so the DC shoud absolutely be scaled to the party's level. They can get it by social skills (diplomacy/bluff), they can get it by picking his pocket, or they can kill him and loot his corpse. What should I set the NPCs skill levels in Sense Motive and Spot to to make it a challenge for most parties? Lets go back to my 10th-level examples. Assume for the nonce that all parties can kill&loot at equal effectiveness, and that all parties can RP for bonuses at an equal level, so we care about social vs sense motive, and sleight of hand vs spot. First of all, I have to deal with characters who have been splitting focus between bluff and diplomacy vs characters who have been focusing on one or the other. Assuming my 10th level example, and assuming the parties could optionally have a magic item that grants +10 to either skill, the range of skill bonuses runs from +9 to +28. That's a 21-point delta, if I split the difference to set the NPCs skill on Sense motive at a 50% chance for the middle (IE, a check of +19), the lower example has to roll a 20 to beat the NPCs 10, whereas in the higher example, the NPC has to roll a 19 to beat the PCs check of 10. In other words, I've bought the worst of both worlds - I am simultaneously overly challenging the PC who has split his skill points between bluff and diplomacy and not picked up feats or magic items to boost the skill itself and not challenging the character who has focused on one of the skills and has picked up feats or magic items. The same goes for sleight of hand (because it is such a niche skill, most people won't max it, but it cant be ruled out). What is an appropriate skill level for the NPC on his Spot check, when facing a 10th-level party?
And there are 2 consequences here - if I set the DC too low, the party doesn't get challenged and shouldn't be given XP for the encounter (if there is no element of risk, it's not a challenge). If I set it too high, it automatically defaults to kill&loot and has the secondary effects of a combat (other enemies alerted, etc).
Whereas in SWSE I can relatively easily figure out what the DC should be. 5 for 1/2 level, plus 0, 5, or 10 for untrained, trained or focused respectively, and +2 for a reasonable assumption about stats. "Base" DC is either 5, 10 or 15 if I want an easy, moderate, or difficult challenge. If I set a middle of the road challenge of 17, that's exactly right for a trained character, the focused character still finds the encounter interesting. If I am worried about an untrained character making the check, I can either bump the DC to 20, or make sure the use of the skill is "trained-only". And in the end, who cares if the untrained character lucks out and makes the check?
One of the design & Development articles (IIRC) talks about how the devs are working on a social challenge system of making multiple checks - that would put to bed my worries about the untrained character making one check by luck, if they have to make several (via roleplaying) to make it through an encounter. He made it once, can he do it again?
