I agree with zomise. With the way the rules are now, one could easily follow the rules and get 99% of the drops.
If I made a grinder in which the items fell into a dropper. The dropper had a button wired up to redstone in such that a player could only press the button every minute and the dropper spits out one drop. The rest of the drops feed on through into my chests. This would be a 100% dick move, but it still follows the current rule of allowing access to the drops of my grinder.