...when cubic zirconias, Swarovski crystals etc look exactly the same?
I'm sure you can tell the difference with the big rocks that some of the slebs wear, but for us mere mortals, what's the point of spending hundreds of pounds on a ring that's identical to one you can pick up for 20 quid at Argos?
Add to that the dubious pedigree of 'blood diamonds' - why do people still want the real thing?