In-car I don't need fast transfers. But when I connect the system to my gigE network to load up the disk or do RSYNC, I do want it to go as quickly as possible.

But speed aside, without an onboard drive controller it would be a bit of hacking and an entirely larger packge/case to fit everything into. I've also not seen any aftermarket cases that are as elegant as the ZBOX. I'm looking at enough customization from a software perspective, so I want the hardware to be as straight-forward as possible.