Okay let me put it this way - even allowing already droppable items to be traded means you are infact creating an economy out of these items, easier just to leave it as it is. You guys think this is all about the income for the company that we don't create a trading system - this would be false.
The reason for no trading system is purely server stabability and security - unless you want to see the entire server got to pot and potentially warrant a reset, i'd just stop asking