First of all, it was not a joke. As the websites presented can show, the Israeli Sex-trade is VERY real. In fact, for more info on this, just go to Yahoo and type in Israel, Slavery.
Now. About the Far eastern workers. Most of them aren't sex slaves, as the perverts in Israel apparently prefer blonds.
Most of them come from the Thai area (Burma, Laos, Cambodia, and Thailand). Some come from China. They are the people who do all the menial tasks in Israel. Sweatshopping, janitorial work, whatever. Most (if not all) 1st world countries import these workers. Israel just often doesn't pay them. To make things better, they are often employed not under Israeli rule but under the rule of their Homelands (China, for instance, where it is illegal to strike).
Now, you may not be able to call these Asians "slaves" because here in America we think of Africans shipped over in chains not happy Asians who are so cheery that Monty Python wrote a song about them. These workers are SUPPOSED to get paid but, generally, they aren't. Their passports are often stolen, too.
For more on this, besides the oh so fun web searches, you can just email Noam Chomsky at MIT ([log in to unmask]) -- I don't know if he'll reply to you but I'm sure he'll enlighten the hell out of you if he does. -- I don't want anyone who thinks he's a nut to instantly cast this off. I found all of this out without reading anything he read, I just know that he knows a hell of a lot about the subject.