Re:Optimised OS X sits on 'versatile' flash (Score 4, Informative)

It's pretty easy to figure out what they probably did: a port of XNU sitting under the most/all the higher level frameworks, and little of the BSD layer except the APIs. And like Joswiak said, thy can cut out a LOT of stuff without crippling the OS or APIs. A sizable chunk of /System and /System/Library can be cut out because it contains support for things not needed on a phone/ipod/internet device, then of course pretty much all of /Applications and that leaves you with a slim, but real, OS X.