Example scenario:
-Boss dies
-Boss loot table contains 3 items (rogue belt, mage trinket, hunter bow)
-All 25 players automatically 'roll' for loot
-Game decides only 9 players will win something, the other 16 win nothing
-The 9 winners are 3 mages, 3 priests, 2 hunters and 1 rogue.
-All 3 mages win the trinket, the 3 priests win gold because the boss doesn't drop loot for priests, the 2 hunters get the bow and the rogue gets the belt
I maybe wrong, but I think this is accurate.