Well I would not judge an adult film star based on films alone. Have to remember that those who have starred in multiple films and are being labeled as "slutty" for doing so are professionals. These aren't girls who were talked into doing porn movies for a few hundreds bucks, but most likely are making more money than probably a lot of folks here make.
So, I don't think you can say "Pornstar X is more of a slut than Pornstar Y, because X has done more work." It may in fact be the pornstar doing less films who is more of slut or who is being paid less that is more of a slut.
I hate to say this, but a lot of these girls find their motivation not so much from a desire to have sex, but from a desire to make a lot of money and gain fame.
Good for them.