I love how HN is some bastion of free-market thinking, but when it comes to items of fashion (aka items that females tend to desire), suddenly supply and demand go out the window, and the pricing of diamonds (and other fashion items) is a vast conspiracy. Horseshit. De Beers monopoly died a long time ago. Diamonds are no more overpriced than any other item of fashion. If you want to buy diamonds at "wholesale" prices there is nothing stopping you.
Cars and shoes depreciate because they wear out. Computers depreciate for the same reason, and more so for the fact that the price/performance ratio of computing technology improves so rapidly. Neither of those apply to diamonds.
Cars aren't worth very much. Try reselling a car to find out how little they're really worth.
Shoes aren't worth very much. Try reselling a shoe to find out how little they're really worth.