Mouseferatu said:
Personally, I avoid this problem entirely. In my campaigns, I give XP entirely as story awards, roleplaying awards, and awards for good ideas and problem-solving, rather than from specific encounters. Seems to work out pretty well for my groups, but I know it's not to everyone's taste.
I actually think that's a very good way of giving out exp, but I tend to think (my opinion anyawy) that you can't have random encounters then.
If the exp for the adventure is Y, and a random encounter happens that's very tough for the players, also resulting in Y, what happens then? Do you stick with your original plan or give them double what you'd intended?
And, if you have 'travel' encounters (when most partys hit random encounters, during travel) planned into the adventure, then they're not 'random encounters'.
So, while I do agree that story based awards are a good way to go, it tends to
not fit with rolling encounters per the DMG.
Regardless, based on the discussion, xp shouldn't be added or subtracted.
Another thing to look at based on the initial scenario is this. An 11th level sorcerer (for example) would provide the same xp when defeated whether or not he uses attack spells or summoning spells. Same with outsiders. They provide a certain xp whether they're able to summon other outsiders or not.
I don't see the initial case as being any different.