I'm going to disagree here, as I think the examples provided are more encounters than relationships. The point of having a one-night stand or a play scene with a stranger at a party is that there is no relationship inherent in either situation. Therefore, they would fall outside the OP's question.
Yes, you can have BDSM without an emotional connection but having someone beat you at a party doesn't mean you're in a relationship with that person. I also think it speaks more to the difference between top/bottom & dom/sub dynamics. I'm not trying to start a definition war! Let alone saying one is better or more right than the other. But the original question was fairly specific in regards to D/s relationships that had gone on long enough to establish trust & feelings over time, not brief encounters.