tangledNlanguid and TantricSoul, you have both said everything I would have so beautifully *sniff*.
I think, truly, the way power is exchanged (and it is an exchange or "flow" as TantricSoul said), is as unique for every relationship as the people who make it up.
For me, I would tell you that my sub has more power because it is his giving of it to me on a constant basis that gives me Dominance. I am only Dominant because of his submission, only because he has given his power to me. And I see part of my job as to make him continue to desire to give his power to me, which is why so much of our play revolves around him (though he doesn't always know it).
I've tried to post this about six times already and I can't phrase it any better, and I do not feel satisfied with my answer at all! *Whew*, what a question, IDCrewDawg!