The steel fist, however, is the term "full range of detterent or security commitments." There's a whole lot implied by that.
The deaths of a couple of million South Koreans, for instance? The steel fist is an empty threat, and the North Koreans know it.
I fully agree that the options are limited in that sense. But it doesn't mean we have no options. A steel fist doesn't necessarily mean mounting an invasion. There are less overt ways to take direct action, and I suspect those will start soon. I'm thinking things like infiltration teams for assassinations and sabotage -- and Li'l Kim's fuzzy head on a platter. Take out the regime, and the rest of NK will roll over.