Lanefan
Victoria Rules
I think the question here might be one of whether the character is under any duress while performing whatever action.What about the many, many spells that don't have attack rolls or saving throws? Why does a thief player have to roll to see if his/her PC can actually perform the movements necessary to pull of a piece of stage magic, or pick a lock, or whatever; but the player of a wizard/MU does not have to roll to see if his/her PC can actually perform the movements necessary to cast a Knock Spell, or a Transmute Rock to Mud spell, or a Polymorph Self spell, or . . .
A Thief is usually under some degree of duress when picking a pocket (doesn't want to get caught); a Fighter is usually under some degree of duress when swinging at a foe (needs to defend); and a caster is often under duress while casting a spell particularly in combat or when danger is near (or expected). In all of those cases it only makes sense some sort of competence check is required, yet only two of those three classes require one.
Things done under no duress e.g. a Ranger setting trip wires or a MU casting an Alarm spell near one's campsite, shouldn't need a check.