I think the UN is using the word "trafficked" way too liberally. While I heard stories from fellow travelers and citizens (only in Cambodia, be careful in Phnom Penh and don't go to Sinahouk); my guess is that the majority of these are in some kind of situation (like owing money to the boss) or maybe justifying what they are doing (it's not a crime if you are forced!).
For some reason, I find this "hundreds of thousands" quite sinister. It devalues the whole issue as it normalizes it; while there are some people now in real need of help and in real danger.