Why can't a set item be the same as another set item? With only a limited number of possibilities of stats to roll, and an unlimited number of the same set item to potentially drop, mathematically speaking it would be plausible to have numerous set items with the same stats.
If these were RARE yellow amulets with the same stats, then I would say you have a stronger argument.
Go to the AH and look up Vile Wards with >294str and 117vit. (Keep in mind those are completely ridiculous rolls - making them worth 1bil gold easily.)
Then note they all have exactly 294str/117vit not one point less or more, and every other mod is exactly the same too. Regen = the same. +Armor = the same. Base armor = the same. All resist = the same.
Hmmm .. and there are 5 of them (at least there were yesterday). What a coincidence!