While there are one or two name-brand AA stars in porn, for the most part the starlets tend to be the white bread, classic "all American" look that we've come to expect. When asked why, porn producers invariably say "because it doesn't sell".
I think, as your post brought out, there are so many psychological and socialogical issues that result in our tastes and attractions, but, for men of a certain age (which face it, many of us are), our sexualization was strongly media influenced, and the "girl next door" look that Playboy fostered was lily white for a LONG period of time. Was it not the Jeffersons before the an interracial committed couple was shown on primetime TV ?
And on the flip side, the attraction of white guys to other ethnicities I think transcends sheer physical attraction. I believe there are underlying psychological issues surrounding "taboo" or "forbidden" lust that are genuine and erection inducing - almost to the point of fetish.
At any rate, an interesting, and thought provoking post - I can certainly understand your reticence in bringing the subject up - but I think the LA board did itself proud, on both sides of the question.