I think its just the way the loot scripts work. The skelly is likely assigned a value of loot, then its weapon and armor and such is selected. The it selects a random item additional, deducting its value from its "total loot" value, and repeating until its 'loot total' is reached. since skellies have a very very small loot table, this can result in multiple of the same item, especially if its tossing copper necklaces and rings.
At least that's how I assume such works!