I don't think the casting of a couple of pornstars has anything to do with trying to "send a message" - most of the viewers aren't perverts like us and won't have a clue who they are. More likely it's just easy casting because a) they know what the girl looks like naked and thinks "she'll do", b) they know she's comfortable being nude in front of a camera crew and simulating sex (if necessary) won't be a problem and c) they know they aren't likely to get a rejection from a Sahara Knite or whoever to be in one of the biggest shows on international TV.
My favourite whore was the hot blonde actress that was giving Jory the eye (how ironic) in s1e5, I forget her name.
That's why they aged Missandei in the show from 11 to around 20.
Yes. Them fucking around with Dany's arc (killing the suddenly treacherous Doreah in Qarth instead of the Red Waste, killing Irri in Qarth instead of not at all, Jhiqui only being in one episode) has left Dany with no confidant near her own age. Although I doubt she'll actually pleasure Danaerys as Irri did, it might seem a little incongruous.
Then again knowing Dan & Dave they probably just saw the chance to cast another decent looking actress in Nathalie Emmanuel who doesn't mind spending each episode with her boobs half hanging out, so they took it.
