The angle I was coming at when I initially mentioned disliking the diamond industry was also because I recall reading that all the world's supply of diamonds are owned and controlled by one cartel who keeps all of them, and only releases them at a controlled rate to ensure that the prices stay high. Obviously if they flood the market with these diamonds, the value would drop and so would their profits.
I don't remember if this was covered in that movie, and I don't have any sources if it isn't, but yeah. As I mentioned before, I shall not be purchasing real diamond when I meet MrsOnyx. If she's the real MrsOnyx, she'll understand and agree, I'd like to think!