Maybe you're question would be better directed at someone who actually works in the porn industry, you need to remember that porn is like any other movie to some extent, it's scripted, actors and actresses are cast and play their roles. Not that I particularly watch porn but modern day porn films will also be using whatever visual effects are available to them as well as acting skills to give the illusion of what you see I'd imagine, for the record I have my heaviest orgasams from deeper penetration so maybe they do cast women who can naturally achieve similar, best of asking someone actually in the industry tho I'd imagine.