A layout like this means you can use both sides of the motherboard for I/O slots. So in a 1/2u box, you can get more than one or two expansion cards in place. The PCI slots themselves seem to be hammock connectors, which I was curious about too, and googling doesn't seem to have any info, unless it's too early/late and I'm missing the obvious.
I know Google don't have a standard rack setup, but still, it would make seens to have all the expantion ports the end of the board... No?