Basic metallurgy. Forged or rolled is stronger than cast. You didn't know that? Apple wants as thin as possible in order to make things as light as possible and allow as much room as possible for parts. Apple also wants it to be strong, and not cost too much or take too long to manufacture in volume (gotta keep the profits up).
The last time I disassembled my Mac Book Pro, the outer aluminum shell was NOT the structural member of the laptop; it was a nice cosmetic cover.
How old is that? Look at the teardown. Do you see anything else that could be the structural component?
It's monocoque. No other structural elements.
I'll get pictures of their production line if you'd like.
That would be interesting, if you're allowed.
Except that the LM claims don't hold up.
The metallurgy is well known. The main problem of this stuff so far in consumer electronics is that it couldn't compete in a commodity market against plastic. Apple doesn't play in the commodity market, making mad profit using more expensive materials and processes. It's a perfect match. The company also had more expertise in its alloys, not in manufacturing, where Apple has ample expertise.
And watch those parts skyrocket in price as the raw material - while readily available
... can be produced almost as quickly and cheaply as plastic.
In the end it has been confirmed that Apple has been playing with these alloys for a while. Then they dumped hundreds of millions for an exclusive license. As a company famous for being stingy on the acquisitions and licenses, it is highly unlikely that Apple doesn't have something very good planned.