I think the reason some things that seem like slight rewordings still sell as rares is that they were historically desired.
Before the days of event items and shard transfers, some of the most desirable rares included server birth glass vials, skull candles, and cauldrons since the graphics were unique. Even though the graphics were later added to the game as common items, the originals still maintained their interest, although they dropped in value compared to items that are still unique.
Not nearly as many people were interested in collecting hay sheaves or sheaves of hay since the graphics were pretty much always commonly obtainable items and therefore no one cared what they were called.
