Certain weapons are spawning in the boxes of blacksmith shops that are too heavy to steal, thus making rare spawns in those chests impossible. Eventually all the spawns will be blocked (if they are not already).
Eeeehhhhh...I would not be so sure about that... Keep checking. You might be surprised those chests can sometimes contain 3 items....
Those weapons are not blocking the rare spawns. They are just always there. When the rare (stacked ingots, wire etc.) is spawned in the chest it will be there as well. http://uorforum.com/threads/the-great-spawning-rare-guide-players-edition.1983/