If diamonds are valued by the 4 C's (cut, carat, clarity, color), what is the value of a diamond that is used in jewelry in an uncut state?

I was looking at the jewelry at diamondsintherough.com and while some of them are pretty (and certainly unusual), I can’t help but wonder if it’s a bit of a scam. I’ve always heard that you don’t know what you’ll actually wind up with until a diamond is cut and polished, so do these have any real value besides speculative? Isn’t the point of diamonds the sparkle? What do you think? Fad, or real value?