I'm actually convinced that the Cauldron of Cataclysm is just using the Charr Flame Altar model just like the 2 Swords are using the FDS model. That would be a lot more plausible than the Charr copying the Cauldron several times for watever reason or the Altar in Crystal Overlook being another 'Ancient Weapon'.
Also, could you think of the origin of the items? The Mists? The Gods? IIRC I read somewhere that Maegdar and Sohothin were created or at least kept in Arah before they were given to the Ascalonian Royalty.