What I recall is that the Ring enhances what is already possessed by the user. Had the Nazgul taken Frodo while he was wearing the Ring at the Ford of Bruinen, he wouldn't have been able to command them, for instance.
No way! Frodo would have kicked all of the 9 around if he wanted to. He was just playing possum to lure them in. ;-)
Anyway, its a reasonable interpretation that the Ring grants power according to stature. I came to my conclusion because I always imagined that if Joe the Random Soldier of Rohan came across the Ring it would quickly corrupt him and thrust him forward to be the leader of his unit, then the leader of an army and then the leader of Rohan. Assuming that no one more powerful managed to take the Ring from him during his rise, anyway.
I cant think of anything in the books to support my position; its just how I always justified it to myself. (And thinking about it, there is probably only one entity in Middle Earth who understands the Ring completely, and he never got to tell his story. "History is written by the victors," and all. ;-)