The purpose of a DKP system is to give people who dedicate themselves to the run the opportunity of first right of refusal of a drop, meaning they can take it or pass to the next highest person. How a person wishes to spend their DKP is upto them. We are not here to tell them how to spend what they earned, except for a few exceptions.
Those exceptions are in consideration of how to best gear up the new group to best ensure success. Even though warriors can use staves, the Staff of Dominance is best used in the hands of druids and casters. Once all the druids and casters have passed on the SoD, sure, if a warrior really wants it, they can have it.
We also encourage people to spend their DKP. Not because that will mean more DKP for everybody else, rather that the better geared the group is, the better chance at overall success for the group. Also, we need people not to be so worried about drops. Over the course of a year in MC, you can be assured that every weapon, every piece of armor, every trinket, every ring, every necklace will eventually drop. And they won't drop once, but many times over (with the exception of Legendary items).
The Leaf and the EoD will drop from Domo's chest. Unlike every other piece of loot in MC, one these two items are gauranteed to be in Domo's chest after every encounter with Domo. Which means, over the course of a few months of farming Domo's chest, every hunter will have their leaf and every priest will have their EoD. This is a gauranteed statement of fact. The question that arises is why is it so important to be the first to get it?
These items differ from the legendary drops because of drop rates. The legendary items are not gauranteed to drop. It could take months on top of months of farming Garr and Gedon to get the two bindings to drop for Thunderfury. I know of guilds that have farmed Ragnoras for the Eye of Sulfuras for 18 months and it still hasn't dropped. Its important to determine who will get the legendary items early so they can start preparing the materials to make the weapons. Where as with the two epic weapons, you are gauranteed to get them. Whether its first, second or eigth, it doesn't matter. Eventually, we will be leaving the EoD and Leaf in the chest anyway (they can neither be sold nor disenchanted).
Every priest can get their EoS right now, how do you verify who got it first? Many hunters have the sinew or the leaf already, how do you verify who got theirs first?