I think a big part of porn's allure over men (and women) is that it allows viewers to experience sex that they cannot experience in their own lives. So while the contemporary range of hotties with the model looks is a bonus, porn is still about the ACTS first and the actors second.

Try going into your local adult video shop and find their "Classic Porn" section...You'll find that ground-breaking knockouts like Annete Haven and Marilyn Chambers were....by far... exceptions to the rule in terms of looks & beauty. Linda Lovelace, Georgina Spelvin, Juliet "Aunt Peg" Anderson and many other porn legends of that era were not known for their beauty, but for the things they did (and thus allowed us to fantasize about doing with them).

I think the popularity of "amateur" and "home made" material is a testament to how "plain" folks would still be as arousing to watch if not more. For example, on this site I personally find the home made facial pictures hotter than the staged 'professional' ones.