It's happening so much because 10 and 25 man loot tables are the same - pretty obvious but thought I'd just point it out in case anyone hadn't realised...
I actually commented on this the other night because 2 weeks in a row Magmaw dropped double swords. I think it would have just been better if a boss could only drop 5 different items off their loot table, no chance for a double drop. Sure, eventually alot of gear won't be needed, but with doubles now, people are getting robbed of drops that could help them.