I understand why people shy away from calling this a gift, but I'm not totally comfortable with thinking of a power exchange as a totally negotiated bargain either. I think that in any relationship people have to make a choice, conscious or not, to trust the other person and to be vulnerable, and to take responsibility for accepting the other person's trust and vulnerability also. Otherwise we would all be walking around in a world of transactions and negotiations. This might be magnified in a D/s setting, but it's really the same in any relationship. Because the D/s interaction amplifies the trust and vulnerability on one side, and the acceptance of responsibility on the other, it is easy to see to transfer as a one-sided gift, from the submissive to the dominant. So submission is a gift.
But I wonder. People have spoken of the gift the dominant brings to the interaction, and of course that's there too - accepting responsibility, being worthy of the trust placed in him or her - but I wonder if the dominant is also offering trust and vulnerability as well. I would think so.