Without opening a massive can of worms or writing a thesis on the matter, I think you have to first identify what "xp" represents before you can justify what gives how much "xp".

If you gain xp for combat, and that xp adds up to levels that provide further combat prowess and additional stats such as health resource, then I disagree that thinking of doing something clever and hitting a button to eliminate a room full of bad guys is equal to or greater in reward than the combat hardening you would get from battling all of them in a face to face encounter.

In contrast, if xp has nothing to do with combat prowess and additional health resource but is instead a literal representation of a character's overall experience as "an adventurer" (for lack of a better term) than I could agree that hitting the gas button and using reasoning to avoid danger and potential harm is as rewarding.

It boils down to the fact I think the title of the thread is appropriate; "Reward Systems". To expand character progression and reward them for doing something more than lifting up a choice weapon and making someone close by bleed you need to implement more than one reward system in a given game. I have always had a problem with the general catch-all "experience" stat; if just thinking of something clever rewaded combat competency and greater stamina/health, then members of political think tanks should be able to go toe to toe with amatuer MMA fighters (yeah, that makes loads of sense there, doesn't it?)

Ultima IV: Quest of the Avatar

Everything I was looking for in an RPG was there. The story, the gameplay, the scale, the spellcasting, the NPC interactivity. Amazing piece of gaming history. It is one of the titles I always end up comparing my own creative efforts against.