Missing the point (again)
Most users want files, therefore they really want a NAS.
Few users need block storage, and typically only for some high end things like databases or sucky email servers (actually, if you know one that does not suck, please let me know), and for most users they would see the SAN through a server which mounts the file system(s) of choice over it.
Cost & reliability are often correlated, but not sucking at something is sadly rare :(
As others have pointed out, you can have block access using iSCSI from a NAS-like unit, so you can have all of them in one device.
Backing up? Now there is an interesting situation, as block SAN has no internal idea of *what* each block holds, so you can snapshot and save, but not on a per file/per user basis, and you can't exclude crud like user's browser cache, etc.
With a NAS you can do both (snapshot and selectively backup/restore).
However, you need it to run a file system and protocol that works for your users, and there are some applications (both Windows and Linux) that seem broken on network mounts due to them not completely behaving like the low level local file system expected. Crap design for sure, but if you must use them and have remote high reliability storage, you may need SAN/iSCSI with your user putting the file system on the served-up block to solve that problem.
Ultimately, you normally want something to keep all key data in one reliable place, and to allow proper protection by replication/backing up so your users don't have to. As they won't in most case know or care until it is too late...