Just to be 100% clear, can you explain how you see the difference between topping/bottoming and submitting/dominating? What is it that would make you consider topping for a relative stranger but not domming them? Thanks.
"Topping/bottoming," as far as I/my partner consider it is that a person choosing to bottom, goes along with what is happening of their own will, and remains passive in decision making, but doesn't hand over the control, or the choices in what happens to the top. Topping, means calling the shots, but not really being responsible for the choices of another. A D/s "encounter" if you will, puts the responsibility for the needs and desires, as well as the safety and well being, of the sub in the Doms hands. As you mentioned, the risks are much higher, both physically and emotionally. Topping is generally how I approach "vanilla" interactions as well.

Clear as mud?