Is it cheaper in the long run?
It sounds great in theory, but what's the cost in terms of switch ports, IP management and cabling? One SAN/NAS can host hundreds of drives, and use only a handful of ports to provide access. There's also a bit of resilience built in, whereas an Ethernet connected drive will need to be protected by application logic.
I suppose these are aimed squarely at the bold new world of cloud ready apps, not my old-fashioned internal data centre ways.