i don't know diamonds as gems in particular but I can guess that branding might make a difference. I can buy a plastic key chain for $1-$5 at some store. I can go to the Prada store and they sell plastic key chains for $600. I'm not going to argue whether or not the design is better, only that that someone is willing to pay $600, I'm guessing to show off they spent $600. And of course that's not even close to the expensive items in the store.