As Don Logan has also pointed out, it could well be that the real issue is that while the set of people who will do hardcore is fairly large, the set of people who closely resemble celebrities is much smaller, and the congruence of those sets is vanishingly small. What got me started on this idea was seeing a fitness model who does bondage stuff named Shannon Kelly and I was watching one of her videos I kept asking, "Is that Kathy Griffin?. They are not really exact lookalikes, but there’s a lot of similarity. (Note: links are head shots only, hence worksafe. For more pics of Shannon Kelly, you can do a Google Image search or go to www shannon_kelly com (replace spaces with periods.)
Sky Lopez reminds me of Kate Hudson at times. (link safe for work).
She’s apparently a christian now, and no longer doing pr0n. 
Muy bonita!
There’s a reasonably well-known porn actress who’s gotten quite a lot of mileage out of being a pretty close Christina Aguilera lookalike, although I’m not so sure how much benefit that would be since Ms. Aguilera hasn’t done anything of note lately…