Quality Flag

Creatures on Vissidal have a loot profile that is modifed by a "Quality Flag," which influences the the liklihood a stat will be on the higher end of the possible range of values. Because several stats need to be in the high range for an item to be considered really good, the principles of combinatorics work to make it far more likely to find a good item on Vissidal than any other place currently.

Django verifies this on Turbine's Forums in this thread: