It's slightly bad wording on blizz's part. Originally, a "win" was 100, but in LFR they changed the rolls to add 100 any roll made by a player of the proper spec to receive the item, resulting in a true "win" of 200. The Needy achievement was never changed to reflect this, so if you are NOT of the correct spec to win an item, you can still get the achievement for rolling 100, but not win the item.