This is as easy to answer as it is stupid to ask. Take The Czech Republic as a representative of Europe, you did single them out in an earlier post, and do a little research;
FreeOnes has 587 Porn Stars listed from the Czech Republic. The population of the Czech Republic is 10,513,209. 587 is 0.005583452207599031% of 10,513,209.
Compared to;
FreeOnes has 5805 Porn Stars listed from the United States. The population of the United States is 317,763,000. 5805 is 0.0018268332058798537% of 317,763,000.
To answer your question, less than one thousandth of 1% of the population of either country ventures into porn. You can get more specific with narrower demographics, but that should give you a good idea.
Thanks for your efforts, but unfortunately this only addresses quantity as a percentage of each population. The question here primarily pertains to QUALITY.
* What we need here are a few volunteers to come forward and put together their Top 10 lists of most stunningly attractive American pornstars, based solely on physical beauty, then compare these women with the list of Euro babes provided in the opening post.