"You have priority to roll NEED on items which are for role that you fill" is unwritten rule since inception of WoW, unless discussed and agreed upon otherwise. What is so unrealistic, what do you can't understand?
greed/de priority is another topic, buy what I said above takes priority. So you have to let some items get DE'd - it's not a big deal, same as letting other role roll. Or hypocrisy much? Don't get mad now, we are close.