I wouldn't trust Platinum and Silver. The platinum supply scenario can change a lot if new deposits are found anywhere in the world, as the total market cap is very low. And silver is mostly used for industrial purposes, with less than 25% of the mined metal being used for investment and jewelry.
Silver's use in industry as well as jewelry and investments in the form of coins and bars is exactly the reason why I buy silver. It has use. It will always have a demand in industrial use due to it's conductivity and reflective properties.