I have a feeling this Studio Display is something else disguised as Display, i mean, it is going expand its functions/role in the ecosystem and so they are charging so much for it.
Perhaps it is the "Apple TV" someone was asking for in the other thread?
Or it is the long awaited update to the 17" Powerbook?
Or they can make it into a wifi router if there is appropriate hardware in there? e.g. DisplayAirPort
Or a thread control for HomeKit - that is easy.
Who knows for sure though, maybe they will have additional plans or it is just economies of scale as the article suggests.