Essentially I think we all believe that Dominant/submissive is an exchange of power but when you talk about it with others there happens to be two schools of thought on it. It can really get confusing because each side believes they are right. I'd like to present to you the two ideas and let you make the decision; who has the power, really?
Before I get started let's talk about power exchange. In power exchange, one person is in control and the other submits to that control. It could be something that fluctuates and evolves or the exchange could happen once and then be maintained that way throughout the relationship. A vanilla relationship likely has a fluctuating exchange that isn't defined but looser. The Master/slave relationship will have defined the exchange at the beginning and then maintain that for the life of the relationship.
Now, who really has the power?
The Submissive has the Power
The submissive camp stands firmly on the basis of the safeword. If a submissive has a safeword then they have the power in the relationship because if they say, "Stop" the Dominant has to stop. They can walk out of the relationship at any time just by revoking the power they have surrendered.
Let's analyze this. The submissive has a safeword. Who gave her that safeword and the power behind it to stop the Dominant? The Dominant of course. That word means nothing if the Dominant isn't going to honor it. You could scream it till the cows come home, but if the Dominant doesn't yield to the power he gave you in that word then it means nothing. So let's dismiss the safeword idea.
Next, the general consensus is that the submissive can just leave the relationship, displaying the ultimate power she has over the Dominant. But wait, does that mean the Dominant can't up and leave? Why would that be? Hopefully, we haven't forgotten that on the basis of a D/s relationship is a relationship. Either party can choose to leave. So that point has now dissolved. What's left in the submissive camp?
The Dominant is in Charge
That's right, in this camp, the Dominant ultimately has the final say in practically every decision that crosses the relationship. When you submit to someone you hand over control to them, whether it be for a short time or for the life of the relationship. You subject yourself to their desires and choices and if they say jump you jump. That safeword you hold on to in some relationships was given to you by your Dominant. Your Dominant has agreed to yield if you use it. (You probably also agreed not to abuse it or it would be revoked.)
So who is it? Who has the power in your relationship? Why?