Those of us who play a lot of Burning Wheel also have a bad habit of using examples from Burning Wheel when talking about Mouse Guard, too. (Sorry, Fuseboy!)
I think that’s the difference you’re adjusting to: in Mouse Guard, character is also very important as a function of the (rewards) system. It’s interesting to me to ponder the differences between the way Mouse Guard represents “character” mechanically, and the way other RPGs do. Many other systems rate “character” qualities mechanically, from Pendragon Virtues to systems like Wraith’s Passions (“protect my children 4”) or PDQ (“Protective Father +2”). Mouse Guard treats them less quantitatively. In other games, the core of your character is represented by some kind of stat. In Mouse Guard, your character’s abilities are rated, but the core of your character isn’t; instead, we have the Belief and Instinct which tell us what lies at your mouse’s heart without numerical trappings. Your character grows and changes according to the situation, as in other games, but rather than a mechanical adjustment, instead you earn artha. It’s an indirect relationship to the mechanics, rather than a direct one.
I don’t necessarily have anywhere I’m going with this, but I’ve always found it interesting and thought you might too.
-B