Because all Demon Scythe monsters don't actually drop Demon Scythes when they die. They drop treasure parcels.
Correct.
Well, at the risk of flaming, they dont really "drop" anything. Your breaking my verisimilitude by using MMO terms.
But I see your confusion now and I will try to give you an example from my own campaign.
I have an adventure path, for lack of a better term, laid out to get the PCs from 1st level to 3rd. As I was writing it I purposefully left out treasure because I wanted to use parcels but wanted to incorporate them into the path in a way that suited my story and my campaign.
So, with the first half written, with an XP budget that takes the group to just past 2nd level, I started puttign together treasure parcels and doling them out to the monsters and other areas within the part of the adventure I had written.
Based on the parcel tables and the suggestions in the DMG (which I do not have here at work) I had 6 items to place, + 2 healing pots + an amount of coinage.
I assembled that into one list of treasure and started placing treasure around the adventure. I did not necessarily keep items and coins from parcels together, I split, and combined and moved and removed to suit my tastes, but the total treasure haul when combined was my list generated by the parcel system.
One item was in a secret compartment the PCs did not find. So, I simply moved that item (since it was a weapon which would figure into their expected items of certain slots) into the next section of the adventure and added it to the treasure list I generated for the 2nd half. so that by the time they were 3rd level they will have the expected amount of treasure for their level. Or at least pretty close +/-, which is as far as I care to calculate.
One of the items was a suti of armor. I put this on a monster in one of the encoutners. Using the chart the monster did not derive any bonuses to his AC for the item, but he certainly got to use the encounter power the armor allowed and this made the PCs aware his armor was "special". And now the party Rogue wears the armor and is quite happy with it.