These are my last five drops, basically one every month since January:
1) Graviton Vortex 5* (LOA) (solo) (treasure room) (Late-January 2013)
2) Graviton Bomb 4* (solo) (Weight of Darkness, during the Kat event)
3) Volcanic Salamander Mask 5* (solo) (second floor of Hazardous Heist prestige mission) 3-17-2013
4) Graviton Bomb 4* (duo) (depth 25 FSC - left side treasure room) 4-28-2013
5) Graviton Bomb 4* (solo) (GIM - treasure room, bottom left side) 5-17-2013
That's 3 Graviton Bombs and 1 Graviton Vortex ?!?!?
What are the odds that i would essentially get the same item 4 times? It seems so unlikely.
Perhaps the items we receive are determined by a combination of actions? Or maybe the location itself plays into it.
That would make sense: Every location where i've found a Graviton Bomb/Vortex has contained either a zombie or a frankenzom.
And the item i found in March (the Volcanic Salamander Mask) was found in a level containing Scorchers.
Another thing to note, i haven't equipped any of the bombs. Is it possible that the game assumes i don't have one yet because i haven't equipped the one i found in January?
I only get 2*-3* item drops and you complaining why you keep getting 4* vortex bomb. Ah my head hurts.
Anyway, back to topic. Random is random. No matter how low the odds are, they are not impossible and if the population size is large enough, it will happen (to someone) eventually.