You'd still want to see what the overall quality of the item is.
That said, it really feels like leather and bone should be generalized while still tracking origin species and creature. I.E. if it's default leather have it actually create a 'leather' object, with the origin tracked internally rather than a separate 'donkey leather' object. It would make noble demands harder though.
Oh, and some leathers should still be different objects (like dragon or whatever that might have a special property)
Honestly, a lot of details in the game seem unnescessary. I wonder if tracking all of that blood and vomit, etc. eats up scarce CPU time?
As mentioned, leather has countless varieties, all vitually identical save minor differences in cost. There is no distinction, however, between thin and thick leather (from cats and elephants, for instance) , or soft and hard (boiled) leather (for clothing and armor respectively). Seems that would be more useful than page after page of pointless leather types doing nothing but making inventory managment a chore.
I suppose this is one of those things put in for Adventure Mode, that don't quite work very well in Fortress Mode.
They may seem "unnecessary" now, but they maybe useful in the future.
Imagine, a legendary +7 goblin mace lord attacked your fortress, killing all but 5 of your dwarves. You managed to drove his siege off, but you know you won't survive the next siege. But behold, one of your lowly recruit managed to nick the goblin mace lord, with the goblin's blood on his blade. So your priest, out of desperation, took the blood and offered it and his own life up to the God of the Bloody Basilisk. In a blinding flash of light and a suffocating cloud of dust, the priest turned into a statue.
Somewhere, a goblin mace lord roared in pain as his blood, and his body, turns to stone.
The statue of the priest is placed in the statue garden, honoured for his sacrifice.