for the most part there is little difference. when it comes it ISCSI SANS
most if not all also have various implementations of samba installed on them so that they can act as both a SAN and a NAS some are even duel NICd so that the SAN network can be dedicated.
if I could remember the one I was thinking of you'd see what I meant.
basically it had a single 1GB interface that you'd want on your corporate network, then if had an integrated 1 GB switch with 4 ports in it to form your storage network.
you can split up the disks inside into multiple disks, (for attaching via ISCSI to various servers (as in SAN)) as well as having more disks that you can share via the samba implementations (as in NAS),
a lot of these boxes also have integrated FTP servers too.
