Got this from Thoorull on Steamwheedle Cartel (EU-H):
This is an excellent observation that's been bugging me for a while. Cataclysm is just around the corner, and everyone will be leveling new characters and doing trade skills from the ground up. It sure would be awesome to have the ability to turn readily available mithril and iron into much harder-to-find truesilver and gold. Let's look into what trade skill cooldowns really do.Blizzard has a long tradition of taking some "special" mats or crafts off of cooldown eventually, to help players along as content progresses. There are many cases: The Burning Crusade and Wrath of the Lich King cloth, Transmute: Titanium, Smelt: Titansteel, etc. What I completely fail to understand is why some now-trivial transmutes are still on a cooldown. Not just plain cooldown, but the all-important one which is used also for current epic gems. This includes vanilla iron, truesilver and essences, and TBC primals in addition to the said current-content epic gems and eternals. It completely baffles me why I can transmute a bajillion of titanium bars or current-content meta gems (as long as I have the mats) but not some old and obscure stuff.