Components on both sides of the board and traces running through the layers of the PCB, just because there is nothing on the surface doesn't mean there's nothing underneath.
I think the most important thing to take away from this is that 512Mb for the OS on Orbis and 3Gb on the Durango means that the PS4 is geared to be a pure games machine, the Nextbox is more the entertainment hub.
I suspect the OS size will hit between 500-1000 on the nextbox by release.
and it'll be able to play custom music during gameplay
I would suspect they'll in fact learn from and use app design from WP and 8, and you'll be able to run apps at the same time as games, in other words. Spotify and similar streaming while gaming.