yeah.. that's what i thought last night..
but like i said up there. i keep forgetting if the ruler can create a new duchy from a town/city with no lord. if they can, then technically.. if you just count the outcome, it's the same thing (though not really RP wise)... and they've "stolen" a region from a duke.
and since they can definitely create new duchy from a town/city with a lord already, they can already "steal" a region from a duke.. so to speak.