These how much would you pay threads are kind of humorous in the sense that the figures in the poll are so unrealistic. No disrespect to the incomes of many providers or the random porn star that tours, these "celebrities" make a lot of money. Like $1000 (high end of the poll) is going to entice Ms. Lilly to bump uglies with Joe Hobbyist?
As for the allure, as I think the OP was getting at I think it comes down to 2 things, beyond the fact that these are attractive women:
1) Trophy Fuck. They are desired by a lot of guys. You got her. "Hey, I banged so & so"
2) You feel like you know them (or their fictional character) & relate to them on an personal level. You really want to "date" say "Rachel" from "Friends" -- afterall you've been watching her for years.