Yeah... what I was talking about was probably 10+ years ago. Indeed now Ameriporn is individual scenes. But that being the case, it has invalidated the original question of OP. AFAIK, Ameriporn scenes are mostly single-actress features. The OP question only make sense if he's talking about the porn industry that was 20 years ago when DVD's (min. 90 mins per title, typically 4-6 scenes with at least 3 actresses for the whole title and less than 50% of all the scenes are 2P (boy-girl or girl-girl). Nowadays it seems most of the porn are story-less (at least plot-less) individual scenes with more than 50% (maybe even 75%?) of the scenes are 2P.
Well... I've already proved that I know very little of contemporary Ameriporn. (amazingly the name Tori Black still rings a bell) But let me try feebly to push back.
The college girls doing a quickie scene seem to rather different to me as a porn customer. I am not very interested in nameless (or nearly nameless) and/or personality-less amateur or "amateur" who make a scene, help me fap once or twice and then disappear. Those I categorize as amateurs and exclude from this discussion. I am only counting "stars" or "idols" who actually make sex vids consistently as a career, for at least a whole year. I only want to count those that achieve name recognition among fans. I keep going back to my (CURRENT) top three... so let's not do that this time. Let's pick some second tier names, Saki Okuda, Aika, Honoka Mihara, Noa Eikawa, Kokone Sakura, Nana Fukada, those names are not everyone's fav, but everyone know of them and JAV practically manufacture recognizable idols every quarter, if not every month. If you use that threshold, I think JAV industry creates more idols than US produces actresses. I don't even think US can come up with a new star every half year.