Anywhere outside of WoW. Because Priests wear heavy leather, or mail, and are usually called "Clerics".
Those blessed carrying out the will of the heavens, on their religious pilgrimages or simply tending to those in need in the calling of their faith. Paladins are Crusaders, there is a difference. :P
Edit: Infact, Blizzard specifically stated during the press release for the original concept of WoW that their "Cleric" was going to wear cloth and be a caster, to be different from what's been done before.