Ok, this must be where the confusion is. It's not a fixed stand, nor one with a simple hinge. They showed just a glimpse of a cutaway of the mechanics and gears hidden in support arm. It's not a lump of aluminum, it's hiding some interesting mechanics.

It's clearly over-engineered, I'm not saying it isn't. In typical Apple fashion they decided to go over-the-top in getting a support arm that "feels weightless, moves effortlessly where you want it, and stays exactly where you leave it." That is not trivial while supporting a machined aluminum monitor housing AND is relatively small.